One other option in that particular situation would be to have left the valve mask on, and then covered it with the surgical mask they provided.

That would (or at least it seems) provide the best protection, as the valve mask protects you (not letting you breathe in anything bad) but opens when you exhale (which lets out anything you might have), while the surgical layer over top stops/slows what you let out through the valve (protecting others) while not doing much for you.

So you have one layer protecting you and the other protecting the rest of the people in the room.

Obviously, not something most would do or go as far as to obtain, but in a situation where both were available...