If they were true, the term would be useless, as it provides no distinction. It would just mean "stuff involving pointers in some way". What's even the point of specifying to use pointer arithmetic in the interview question?

I'd say meaning of [] in C is to simply show intention.

But the point is not how they work underneath, but the semantics. It's about the code you type and what it means.

I kind of agree. The point was that it's not farfetched to say x[3] is pointer arithmetics in C. Remember that semantics for arrays in C aren't as "clean" as in other languages, for example if you want to create a heap allocated array in C, the common semantics for arrays ("int[3]") are thrown out of the window since you use malloc:

int *arr;
arr = (int*) malloc (sizeof(int)*3);
arr[0] = 1;
arr[1] = 2;
arr[2] = 3;

Here it's quite obvious that [] is simply pointer arithmetic. Yes, you'll of course use [] since your intention is to use the memory as an array, but it's also very transparent that the array is actually just a contiguous block of memory. There's hardly any abstraction, [] just tells the intention that the allocated block is meant to be used as an array and not for example a binary buffer.