It could have been something that got caught in the belts, or the belts themselves. I'd have the timing belt looked at as well. You'll have to remove the valve cover to get a look at it or take it to a mechanic.

If your temp gauge wasn't showing overheating then I doubt that's the problem unless your gauge is malfunctioning. What was the temp when it happened? Let the car idle for a while and see if it does it again. If not, it probably wasn't overheating.