Popcorn damage teeth + gums?!

I don't know. I think, though, the popcorn itself is not a problem. What sticks around is general the tough, fibrous stuff that is not very nutrient rich, so not likely to cause excessive bacteria. Of course, you also have to take into account the stuff you put ON the popcorn, which is not only worse for you, but probably worse for your teeth as well.

All in all, I don't think it's a big deal for a few hours. Maybe you could take some sugarless gum with you... chewing that will dislodge a LOT of it.

Popcorn is the worst for getting stuck at your gum margin and between teeth. It will not cause harm if left for a while until you get home and use floss but if it is left there for days then it can irritate your gums and cause them to swell up.

I am a dental nurse in Oral Surgery

Not a problem as long as you do clean your teeth and floss when you can...You may get a little gum irritation however. Good luck and I wish you well.
The Denture Pro.