Strikes me that the child is repeating what he has been told, kinda like going into a china shop and saying "No Touching, No Touching, No Touching."

While the particular dog you had might be a sweet dog who only hurts fleas and other invertebrates, the small child's caretakers have probably indoctrinated him not to run up and pet strange dogs that he comes across.
I know that I instructed Little Bear in this way when he was very small, because I didn't want some random mutt to bite his face off when he was just trying to be friendly.