I have not seen that one but have seen them do strange things to strange objects.
Some like to rub against things like sneakers,or a stuffed toys.
I would think he saying "I like this and it's mine".
I Know a gal who's chin would pee on her and she trained her to stop.
You could see anything from them.
It does sound like it's pleasing him.
I would try and stop the peeing if it were my chin.