Puppies do bite. It's one of those things that you need to be persistent and consistent about. Eventually he will catch on. My dog took until she was 2 1/2 before the play biting stopped. Now a simple "no bite" command stops her.
One thing I've learned is never tease your puppy with your hands. Don't play hand games. It only confuses them. If you are playing, grab a toy and let him bite that. This way he will learn it is okay to play, just not with your fingers. Puppies do forget sometimes. They have a habit of mistaking toy and fingers. And, they sure do have sharp little teeth!
As for the accident and him biting you, I agree with the others that it was out of fear. My dog will do this sometimes. What I try to do is to remain calm and talking soothingly while I work through whatever it is. The more your energy raises, then more they will panic.
