does he bite down on his hand each time or most of the time or did it happen once. he may not have meant too. I have found that some babies do stuff like that because they dont' know how to express themselves they get upset because they don't know how to deal with certain emotions and act out like that, I have a nephew who did stuff like that as a baby. it will probably get better as he gets older.
It doesn't happen everytime, but every once in a while, when he gets really angry. It made me so sad one day, I was thinking about it all day. I couldn't get the expression on his little face off my mind. He just looked so frustrated and angry. Thank God, he doesn't have any teeth, or he would have really hurt himself.
I do hope it goes away.