Meh. It happens to me randomly as well on different games. No big deal. Probably just an unhandled exception type error that the system can't deal with and reboots itself.
Kudos for that, it has happened to my PS3 when quiting random games since I've bought it in 08. Probably something along the lines of what you said.
This will happen to you alot, sometimes it happens to me upon entering a game. Since them 4.0 patches that is.