Greg Bailey wrote:

Is there any chance someone could have hit the ctrl-alt-delete key combination on the console to trigger the reboot? I've had people do that inadvertently thinking they were on a Windows machine...

After rebooting servers 3 or 4 times that way myself, I now disable this function in /etc/inittab on all of my servers. I don't see any point in allowing a hot-key to reboot a server.