It's really just the same kinda thing that fills most coding interviews (that aren't just pure live coding challenges): the interviewer is testing for something that isn't directly relevant to the role, because of course in the real role you'd be able to (and should!) research all the appropriate meta tags you should have on your web site, but since the interviewer deems it too difficult to actually directly test for the ability to do the job, they instead test for things that surely the candidate must have ran into before and has a good enough memory to at least have a conversation so that I can subjectively judge how skilled the candidate is.