Glad he's OK.
It's worth a shot to keep an eye out the next time he gets stung - I have a friend who reacted mildly the first time she was stung, went into respiratory failure the second time. She's now had a primary and secondary immune response to the venom protien. I could go into the biology of it, but in essence the initial response is a few cells saying "aww hell, something's here that shouldn't be" and the secondary response is "aww hell, it's back, call the national guard!". In between the two responses you have what amounts to an APB being distributed throughout your immune system, so the second ONE cell responds to ONE antigen, *poof*, it's all out thermonuclear war against the invading party.
This is part of why H1N1 and H5N1 are so deadly - the thing that kills you is the off chance of a cytokine storm. Your immune system goes ape sh** and fries/pickles/fricasees your internal organs.
I always keep benadryl and some topical steroids around as they can buy you time to get to a hospital. Epi pens are great and should be part of any kit belonging to someone who doesn't know about their bee sting reaction status, or if you intend on being able to help out others at events and such. In a non bugout situation, my BOB goes with me all kinds of places, including the range, since I have all my junk with me, I could help someone out that got injured. Even if a folding stock just breaks and busts an upper lip, it's nice to stop the bleeding long enough to get someone to the ER.
Thanks for the reminder to get a fresh epi pen along with my suture kits!