K.N.
I think the way to put it is "sometimes your brain doesnt see words right and this special class will help you teach your brain what to do with the letters on the paper in front of you." Everyone is different. There is noting WRONG with people with blue eyes, even thought most have brown. You cannot help it, it is nothing you did wrong, but we need to help your brain understand things better. The teacher of that class or a counselor or the reading specialist may have suggestions on this too.
Good luck! I am glad he is getting help so early