It's possible to get an upset stomach from anything- if he's intolerant of certain foods, then it'd be possible. Like if I'm allergic to shellfish, I could get very sick and even die from eating even a small amount. Or if I'm lactose intolerant, ingesting lactose could give me an upset stomach.
But no, he didn't develop gastrointestinal illness from your homebrew. He had a bug of some kinds.
I've heard of a few people who drank really young sediment-filled beer (really yeasty) get diarrhea when they overdid it, though. But it was much later, like the next day, and not within minutes.
Even food poisoning (which is NOT what happened here, but as an example only!) takes about 24 hours to show symptoms. So whatever he had was in his system for a while, at least a day or so, unless he's allergic to beer.