C++: Semantics of [x] for dereferencing: C-style vs pointer array

I know that a c style array is stored as a contiguous block of memory. That is why the following code:

int main (int argc, char *argv[]) {
    int arr[3][3];
    *(*arr + 5) = 5;
    std::cout << arr[1][2] << std::endl;
    return 0;
}

prints 5. I assume that for c style arrays *(*arr + 5) = 5; is roughly equals to the code which the compiler produces for arr[1][2] = 5; isn't it? (Q1)

If so, then the semantics of arr[1][2] (i.e. shifting on one block of memory) is totally different from doing the same on a multidimensional pointer array where every level of nesting results in a pointer being dereferenced. Is that right? (Q2)

Is there any situation where I need to pay attention to that myself? I.e. where the compiler does not know himself what kind of array he is dealing with? (Q3)

(Qx marks my questions)

Thank you in advance and Regards