I have had 2 to explode. First one was in my wife's car. She had gone to lunch from work and when she tried to crank the car at the restaurant she heard a muffled boom and smoke came out from under the hood. The hood was buckled and the underside was covered with acid. Believe it or not the place where we bought the battery paid for the repair on the car and replaced the battery. It was only a month old.
Second one was a 6 volt golf cart battery in my motor home. I used two in series for the coach components including the generator. Went to start the generator one day and heard a boom and one of the Interstate's blew it's whole top out.
Lucky like you that I was not in the line of fire (or acid). These guys can be really dangerous in the right conditions.
Glad it was not any worse for you.