I think there's zero excuse to be rude to candidates, and the 101 of interviewing is to make it as comfortable as possible for the candidate and not hurrying them up when they are thinking (which wouldn't rememble real work anyway, those aren't the typical time pressures one usually finds on the job... usually). You want them to succeed and not trip up; if anything because it means no more conducting interviews for you! Also, basic human decency.

That said, really... finding a trivial python function using google search, that is a real life work skill. It's 100% real and not made up for interviews. I guess these days one would ask the LLM, too. The only artificial thing was the time pressure which, granted, complicates things needlessly, but other than that, the fact the candidate didn't come up with an answer is still a red flag. (I wouldn't disqualify them just for this, but maybe there were other red flags already?).