Can the mods require a poster to reply to a question?

I think you were justified and handled it very well. I would have preferred if you gave the explicit rationale alongside the modhat request:

Just so that people who haven’t been following the whole thread know right then and there that you suspect him of trolling. As opposed to, putting on your modhat just to tell him he’s wrong in P&E (in context, you clearly did not do that).

~Max