LOL, I think it is because your dog is a rough coat/short coat border collie. People are too used to the long coated border collie. Someone once asked if my friend's german shepherd was a mix because he is a long haired shepherd. He is also friendly with strangers if my friend is with him and is relaxed. Otherwise, the dog will alarm bark if he doesn't know you or if he's seen you a lot of times would run at you and hump your leg. This dog is two faced because he will allow the neighbors to pet him if my friend is around but if not, he would hump the guy's leg like crazy if he goes up to him.