why does pushing an item into a data array not update the view/vuejs dev tools with the new data?

For some reason, pushing data into an array doesnt update the view/vue dev tools data. Why?

I have cleaned the browser cache without any luck.

theArray = [
   [
      {
         test: true
      }
   ]
]

methods: {
   addNewItem() {
     console.log(this.theArray[0].length); // = 1

     this.theArray[0].push({}); 

     console.log(this.theArray[0].length); // = 2. This does however show that the data was pushed but why do the view and vuejs tools not update/show the pushed data?
   }
}

However, doing this works for some reason?

this.theArray.push({});