Did you bottle condition the beers at a higher-than-room temperature. If you're bottle conditioning temperature was higher than your buddy's, not only would it have carbonated more quickly, but any infection would have grown faster. Your buddy may be in for a surprise in a few weeks.
If the ONLY difference is the bottle conditioning temperature, I would have to guess it's the culprit. Especially, if he has stored his at cooler temps after conditioning.
perhaps a line of single hop IPA's - there's so many new hops out there!!!