I'm not defending this dude at all but some people just like it. My girlfriend has explicitly told me that she likes when I grab,/squeeze her neck. I'm also not a mansplaning douch though.
Same reason for mine. That's why I often times will just grab her shoulders and lightly squeeze for a bit if we just have a minute and we're waiting for something. Easy to do and she enjoys it.
I feel like the guy standing over the girl at a party with his hand on the wall above her head - to show "ownership" - is even more representative of the species.