The tube blew but the tire was fine? Interesting. Sometimes if the tire is faulty, the tube can blow out through the weak spot. But I've had this happen, once just after I picked up my current car at the dealer and was on my way home -- I got about a block and there was an explosion from right behind me. My initial thought was that there was something wrong with the car, but then I realized it was the bike tire. Was it considerably colder when you pumped up the tires? That can be a factor, you get the pressure right when it's cold, but then the day warms up and riding on it causes additional heating, and the now overpressurized tube blows.