If a strange man insisted on putting his arm around one of the Disney princesses and kept trying to do it after she told him to stop, would it be OK?
I think that's sort of equivalent to what's gone on here. Not sexual but invasive, and crossing personal boundaries.
No, a man's pecs aren't anywhere near as sexual as a woman's breasts - but do you believe that body autonomy only counts when it comes to areas which are considered to be sexual?
If a customer at work kept stroking your upper arm even after you had told him to stop, would that be OK? Or should you have the ability to say "I don't like that, please stop"?
I mean, obviously the answer is that you should be able to tell them to stop touching you. No part of anyone's body is there for another person to touch however they want. Your body, your decision.
Playing devil's advocate.........I've seen this Gaston in other videos and he plays the role brilliantly - he really hams it up, and talks about his amazing pecs and chest hair and what a manly man he is (ie/the Gaston character perfectly!). Trying to be generous, MAYBE the woman had seen this larking around and thought Gaston would be OK if she placed her hand on his pecs (there is a video where he invites another woman to touch his pecs). But when he tells her to stop, and she carried on, then that's where it becomes deeply problematic. I'd have been utterly mortified to have misinterpreted something so badly and wouldn't be able to run away fast enough. And to be fair, this is a very generous possible explanation based on viewing the shortened version of the video. I don't really think you should be touching another person, even when they're playing a character, unless you're explicitly invited to. I'm just trying to think of a possible alternative explanation.
Body autonomy matters. I reinforce to my DC that they don't have to be hugged, or be touched on any part of their body at all if they prefer not to be.