I (M17) feel weird when my girlfriend (F17) get's touched inappropriately by her friends

Me and my girlfriend are very close and always touch each other (but not inappropriately like we do stuff like interlocking legs, holding hands, laying on shoulder. that type of stuff), but one time I was scrolling through Instagram and I see her getting humped as part of a "tiktok dance" by one of her friends (who is a girl and recently befriended like 2-3 months ago) and I felt really weird about that and uncomfortable. When I told her about it, she said "it doesn't mean anything if I have no attraction to her", "it was just a dance" and I tried my best to explain to her but I guess it wasn't being understood. Am I valid for feeling this way? Is this a good or bad thing? Your advice is appreciated !