The 78XX or 78LXX devices are extremely rugged, They are uncondiitionally stable and will not oscillate even without external caps, unless you drive a reactive load with them. I always use external caps to reduce noise, but they are not required for stability.
I'll wager it was blown out by a voltage transient. Car electrical systems have lots of them, and most electronic devices should be protected by at least a series resistor and power Zener if you want them to live, adding a cap across the zener also helps reduce the pulse amplitudes. A Tranzorb is even better than a zener for clamping protection.