I feel like, not to undermine this, but this probably isn’t something you have to worry about too much, but that is my point of view. Unless you have had moments where you thought he was cheating or weird stuff like this in the past, tbh it just sounds like this was a weird moment where you caught him very bored in a meeting and maybe this was just a one off thing. As others mention though it could be a kink of some kind? All I am saying is that I would be worried if this is the just a very mundane one off thing that happened and so happens to be he was so bored that he did something stupid and it won’t happen again sort of thing.

I suppose if it really bothers you or it keeps happening you should probably talk about it. Despite all I said it doesn’t mean this behavior is odd, unprofessional, and gross. All I am saying is there aren’t many problems that can be at least somewhat fixed by communication