What would cause this to happen to a preamp?

Yesterday I was at a friends house listening to his system. At one point we noticed that the soundstage shifted left a bit so my friend decided to check the xlr connection to his amp. While the music was still playing, he jiggled the xlr cable at the amp which caused a brief sizzling sound in the preamp. The preamp then shut down. Obviously we were pretty bummed out and concerned. Pushing the power button on the preamp would not power it up. We checked the fuse and it was fine. We then tried disconnecting the power cord and reconnecting it. The preamp then powered up fine. We listened for a few more hours and it sounded fine. So my question is...

Why would "jiggling" the xlr cable at the amp cause the amp to shut down? What happened? Some sort of short?

Thank you...