My neighbor has a boa constrictor that I help him wash. No relation to Steve McQueen. He also has a rosy boa thats bit me a few clean-ups ago. I'm no snake expert but that little guy has a mean streak
Snakes, like people, have personalities. Some are laid back and some are cranky. Maybe your neighbor's snake is one of the crabby ones! The upside, constrictors aren't poisonous!