[_yawn]

The whole point of abstract data types is to separate implementation from interface in order to allow a change in representation.

The point is to allow programming things like the AI algorithm without caring at all about if the board is represented with a hash map, nested arrays, or a bitboard. In all cases, all the AI cares about is move generation, not internal representation.

Abstraction does not hinder ideas like the bitboard, it enables them. Both the interviewer and the interviewee are missing the point.