I've had FWCs pushing 9 feet and 8 lbs. and as thick as my wrist. I'm not a small person.
I was NOT shocked when I was bitten by one of my FWCs. There goes THAT blanket statement.
Were you aware that appx. 25% of bites by venomous snakes are dry? Ever think that may have been why there was no reaction to the copperhead bite? A puncture wound will cause localized swelling. Two would cause more. Hmmmm, wonder if that's what happened?
Unless I'm mistaken, there is some difference between insect venoms and reptile venoms. I'm not positive that an allergic reaction to one would indicate a predisposition by a bite from the other being deleterious to the one bitten. It could be, but I'm not in possession of any knowledge to back that up.
Do you happen to have a picture of what your friend says is a brown recluse? If he is truly immune, I suspect there are some venom research facilities that would love to meet him.