Dogs look at this different than we people do. My little Chipper usually sniffs where he potties, but he does not lick it. However, if one of the girl dogs goes to the bathroom, he not only sniffs, but often licks a little . I think it has something to do with getting her scent on him. A dog thing, anyway.
A billy goat is totally disgusting, he not only pees on his goatee, and licks it, then he rubs it all over himself. It is all a mating thing.
I have no idea why your dog is doing this, and it is good to have it checked out, but it might just be a habit he has gotten into doing, and just scolding him when he does it might help him break the habit.
If having a soul means being able to feel love and loyalty and gratitude, then animals are better off than a lot of humans. — James Herriot