Could be, I thought she got a funny look on her face and moved away from him, and then he made what could be a compensating and cover reaction, by moving over and putting his hands on his girlfriend.
Both of their body language reactions, support your idea.
Watching it again, I see that she clearly jerked away from him.
Yes and I’m trying to figure out why there was a sudden jerk... if you look up until that moment you can see his hand reach behind her, which is nothing abnormal at first glance, but then a few moments later she jolts. Why did she jolt? Did he pinch her butt? Did he grab (read: manhandle her) after she said she preferred his conservative brother more (which was obviously her joking around)?