I hope your boy's memory of it will be that the seal liked him enough to play with him, even if it (rightfully) freaked him out at the time. Most folks don't appreciate what a good set of choppers seals have........but I've seen them bite right through the fiberglass on a surfboard.
I've had one do a friendly nibble on my arm, and knowing what kind of teeth they have
a) made me impressed that the seal could be so gentle and not leave a mark on my wetsuit
b) made me pee in my wetsuit, even if I'm not in the pee in your wetsuit camp. I know you are of the opinion that EVERYBODY pees in their wetsuit, but honestly when you're around critters that can smell 1 part pee per billion parts water I think it's probably a good thing to resist the urge.
Getting even a friendly chomp in the water is enough to make anybody extrude.