I think I said something about the stack efficiency. I was a kid that barely understood out of order execution. Register renaming and the rest was well beyond me. It was also a long time ago, so recollections are fuzzy. But, I do recall is they didn't prompt anything. I suspect the only reason I got the interview is I had done some SSE programming (AVX didn't exist yet, and to give timing context AltiVec was discussed), and they figured if I was curious enough to do that I might not be garbage.

Edit: Jogging my memory I believe they were explicit at the end of the interview they were looking for a Masters candidate. They did say I was on a good path IIRC. It wasn't a bad interview, but I was very clearly not what they were looking for.