Yikes, that actually triggered me - the way he puts his arm like that around her neck - the abusive ex used to do that. It's one of those 'Sleeping With The Enemy' moments, where to other people it looks ok, maybe a bit possessive, but you know, just KNOW that he's reminding you that when he's no in public he is going to make you pay for whatever you've done.
Sometimes they just do it with no follow up. But it makes you stop in your tracks anyway. Look at how her eyes change.
Yes, it's only a flash of anger from him - but that flash is all it takes to put an abused person in their place, especially with the 'controlling arm' follow-up.
I'm worried for her too.