+1 either it wasn't degassed and had too much CO2, or they bottled too soon and there was a little fermentation in the bottle. If it's the latter, I'd worry about bottles breaking or corks being forced out by the pressure if it is still fermenting. If I were him, I'd carefully uncork another one and see if it's the same way. If so, maybe he could uncork them all and recork them to relieve some of the pressure?
"Science + beer = good!"