sqrt and its approximations seems a bit too low-level, both for what he did and what Facebook is doing. This is the kind of stuff you look up, as opposed to other algorithmic difficulties that arise out of total different situations where without a good general background you wouldn't even know what to research.
Questions about trees, graphs etc. would seem more appropriate for game development (and probably for Facebook in general).
But that's just me. Sqrt might even be a good question if he's a recent graduate and they want to see if he still can think back a couple of years...