Assuming the quoted wording is the actual question he gives, it's not ambiguous. With the given wording, a person hearing it and understanding that it's stated precisely without ambiguity shouldn't be dinged for not questioning the interviewer's ability to recognize the requirements are unambiguous. Because it's an _interview_ by a technical professional who thought about the problem beforehand and not someone who you should be worried about not understanding what they are asking. In fact, I can imagine another interviewer that would ask you the exact same thing and ding you for asking a stupid question.

Interviews are just not the same thing as real life requirements gathering, so people's thought processes will not be the same. Even if you try to roleplay as someone that doesn't understand how to state requirements precisely, all of the normal procedures and thought processes for sussing that out are compromised due to the inrerview setting. And your ability to assess those processes are compromised due to how familiar you are with the question and how much you've deconstructed it.

It's not the time to be tricky (though somehow simultaneously believing it is and is not a trick question). There's so many more interesting things that could be gleaned from a person's interview performance that "is this interviewer playing fuck-fuck games with me" doesn't rate whatsoever.