What does it mean if you put your hand on top of someone's head?

So, a few days ago I was at someone's place. A certain person comes in and puts his hand on the host's head (the host was seated) and says hi to the other guests (shaking hands with some).

I found this pretty offensive. Putting you hand on top of someone's head is basicly saying that you're above that person. What makes it even worse is that he did it to the host, and shaked hands with other guests.

Then I found out that he has done this at another place, also putting his hand on top of the hosts head. I think it's just plain rude.

Am I overreacting here?