How very rude of him. I would have said something right back
That's one of my pet peaves (no pun intended) is when someone comes up and just pets one of my dogs without asking. what if they were to spook them and they bit whose fault would it be, mine. I've always taught my children to ask before they pet anyones dog.
We had a little girl ride up to us on her scooter the other day and drop the scooter and ran up to my 65 pound mutt and started petting him. Luckily he's use to kids but what if it had been a dog who wasn't.