Stories like yours and the grandparent comment give the impression that there is little communication actually happening in an interview. I guess if it was an at home assignment given in an email you might not know what the interviewer wanted, but in an actual in-person interview why wouldn't you just say "Well, you could do String.reverse(), is that what you're looking for[?], or would you like me to implement a solution without using String.reverse() or some other way?"

And on the other side, if the interviewers are looking to identify whether a candidate knows about String.reverse() and the candidate starts writing out some 20 line algorithm on the whiteboard, why would you just sit there and watch instead of being like "actually, we're looking for something else, let me ask it a different way; do you know how to reverse a list using the standard library? We're looking for a one-liner here, not an full algorithm implemented on the board."

If your story is true, then apparently there are at least some interviewers willing to just sit there while a candidate writes out 2 completely different algorithms on a whiteboard without interrupting and communicating what they actually want. Such an interviewer is either socially incompetent or trying to make a fool out of the candidate. Either way it doesn't reflect well on the company.