The "in" operator is not unusual or trivia, it's something people who code in python use all the time! Python does have a function (or more accurately a method), it's called __contains__ and it's invoked by "in". I would expect a python developer to be able to comment on whether python uses a fastsearch algorithm or not, they should be able to comment on BM and H algorithms.

Maybe this was a very junior position, but I'm with the interviewer here. Using regex would be very questionable - and a solid case of 1171.