But I think he was wrong to expect people would rearrange their seating for him. Regardless of what I think of that stricture, it was on that guy do adapt to the situation. Not everyone else to accommodate him.

I agree.

Also, as a point of interest, since it revolves around menstruation, could he ask "are you on your period", and if the answer is "no", could he then sit next to the woman?

Probably not. It's not just whether they're menstruating - there are rituals that have to be completed before Niddah is removed, which a non-Jewish woman would not have undertaken. And of course, that's a deeply personal question that many (most?) women would feel uncomfortable answering, and which some women might even be offended by - which is both an unkind thing for the orthodox Jew to do and should make him feel uncertain that the person he's asking would always answer honestly.

One feature of Judaism is that there are many commandments that the Torah not only prohibits Jews from violating, but also prohibits them from coming anywhere close to violating. For example, during the spring festival of Passover, Jews are commanded to refrain from eating or possessing certain grains (wheat, spelt, barley, oats and rye - collectively "chametz"). But the prohibition against eating or possessing chametz is so important that Ashkenazic Jews will also refrain from eating or possessing corn or beans or other legumes (collectively "kitniyot"), in order to avoid even the slightest possibility that food that they believe is kosher for Passover might contain some trace of chametz. Which is why some very observant Jews will engage in behaviors that seem only marginally connected to complying with a specific Torah commandment, because various Talmudic or other interpretations have found that the behaviors are necessary to avoid even the risk of violating the relevant commandment.