Weirdly anti-intellectual. I'm not sure what the subtle nitpick the expert brought up, but from reading the comments I gathered that they correctly pointed out that appending to a vector is merely amortized O(1), not truly worst case constant time. This is actually kind of a big deal and is an important distinction to make. As a corollary, it means you can't just use a vector as a constant time sequence data structure in a real time application unless you preallocate it.