What an insulting interview question, I hope it was just in jest or at the end looking to pad the time
However, it did make me realize hidden therein is an actual interesting interview question, similar to the "describe what happens when you type an address into the browser's URL bar and hit enter": describe what happens after you type `:s/foo/bar` and hit enter. Followup version: what about `:%s/foo/bar`? The kind of thing that can be interesting to watch them reason through even if they don't know the answer, or even know what those syntaxes do.
Q: "How do you do a search and replace for a string in VI"
Me: I cant recall right now, i'd just google it"