When 2 was young our neighbors had a husky that would do the same thing. Calm as could be, tail wagging, he would let you walk right up to him, but once you were within striking distance (he was on a chain), he would come unhinged and try to take a piece out of your hide.
Had a German Sheppard male guard dog at dads shop. Nicest dog you would ever met. He would let you walk up and pet him, tail wagging, just sitting there minding his own business on a chain. Once you were finished petting him and you turned around to leave, he would nail you in the calf or hamstring.
I don't know how many people I had to tell to "back" away from the dog. I learned my lesson to not walk up and pet guard dogs as a kid. Only took once.
Granted the dog that bit the OP was not on a leash and should have been.
