Why does Laravel read the schema as if it had 2 primary keys? [duplicate]

Here's my laravel composer.json for its version info:

{
    "name": "laravel/laravel",
    "type": "project",
    "description": "The skeleton application for the Laravel framework.",
    "keywords": [
        "laravel",
        "framework"
    ],
    "license": "MIT",
    "require": {
        "php": "^8.1",
        "guzzlehttp/guzzle": "^7.2",
        "laravel/framework": "^10.0",
        "laravel/sanctum": "^3.3",
        "laravel/tinker": "^2.8",
        "laravel/ui": "^4.6"
    },
    "require-dev": {
        "fakerphp/faker": "^1.9.1",
        "laravel/pint": "^1.0",
        "laravel/sail": "^1.18",
        "mockery/mockery": "^1.4.4",
        "nunomaduro/collision": "^7.0",
        "phpunit/phpunit": "^10.1",
        "spatie/laravel-ignition": "^2.0"
    },
    "autoload": {
        "psr-4": {
            "App\\": "app/",
            "Database\\Factories\\": "database/factories/",
            "Database\\Seeders\\": "database/seeders/"
        }
    },
    "autoload-dev": {

        "psr-4": {
            "Tests\\": "tests/"
        }
    },
    "scripts": {
        "post-autoload-dump": [
            "Illuminate\\Foundation\\ComposerScripts::postAutoloadDump",
            "@php artisan package:discover --ansi"
        ],
        "post-update-cmd": [
            "@php artisan vendor:publish --tag=laravel-assets --ansi --force"
        ],
        "post-root-package-install": [
            "@php -r \"file_exists('.env') || copy('.env.example', '.env');\""
        ],
        "post-create-project-cmd": [
            "@php artisan key:generate --ansi"
        ]
    },
    "extra": {
        "laravel": {
            "dont-discover": []
        }
    },
    "config": {
        "optimize-autoloader": true,
        "preferred-install": "dist",
        "sort-packages": true,
        "allow-plugins": {
            "pestphp/pest-plugin": true,
            "php-http/discovery": true
        }
    },
    "minimum-stability": "stable",
    "prefer-stable": true
}

My Student migration:

<?php

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

return new class extends Migration
{
    /**
     * Run the migrations.
     */
    public function up(): void
    {
        Schema::create('students', function (Blueprint $table) {
            $table->id();
            $table->unsignedBigInteger('identification_number')->unique();
            $table->string('name');
            $table->integer('class_level', 3);
            $table->string('major');
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     */
    public function down(): void
    {
        Schema::dropIfExists('students');
    }
};

My Student model:

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use App\Enums\MajorEnums;

class Students extends Model
{
    use HasFactory;

    protected $fillable = ['identification_number', 'name', 'class_level', 'major'];

    protected $casts = [
        'major' => MajorEnums::class
    ];

    public function AspirationReports()
    {
        return $this->hasMany(AspirationReports::class);
    }
}

Error log:

(base) evanfersadi@pop-os:~/Dokumen/School/pengaduan$ php artisan migrate:fresh

  Dropping all tables ........................................................................................................ 27ms DONE

   INFO  Preparing database.  

  Creating migration table .................................................................................................... 4ms DONE

   INFO  Running migrations.  

  2014_10_12_000000_create_users_table ........................................................................................ 7ms DONE
  2014_10_12_100000_create_password_reset_tokens_table ........................................................................ 4ms DONE
  2014_10_12_100000_create_password_resets_table .............................................................................. 3ms DONE
  2019_08_19_000000_create_failed_jobs_table .................................................................................. 8ms DONE
  2019_12_14_000001_create_personal_access_tokens_table ....................................................................... 5ms DONE
  2025_11_24_064503_create_students_table ..................................................................................... 1ms FAIL

   Illuminate\Database\QueryException 

  SQLSTATE[42P16]: Invalid table definition: 7 ERROR:  multiple primary keys for table "students" are not allowed at character 164 (Connection: pgsql, SQL: create table "students" ("id" bigserial not null primary key, "identification_number" bigint not null, "name" varchar(255) not null, "class_level" serial not null primary key, "major" varchar(255) not null, "created_at" timestamp(0) without time zone null, "updated_at" timestamp(0) without time zone null))

  at vendor/laravel/framework/src/Illuminate/Database/Connection.php:829
    825▕                     $this->getName(), $query, $this->prepareBindings($bindings), $e
    826▕                 );
    827▕             }
    828▕ 
  ➜ 829▕             throw new QueryException(
    830▕                 $this->getName(), $query, $this->prepareBindings($bindings), $e
    831▕             );
    832▕         }
    833▕     }

      +9 vendor frames 

  10  database/migrations/2025_11_24_064503_create_students_table.php:21
      Illuminate\Support\Facades\Facade::__callStatic()
      +36 vendor frames 

  47  artisan:37
      Illuminate\Foundation\Console\Kernel::handle()