If there was a problem, it would be with the amp, not with the subs. You
have
them wired at 2 ohm mono, and your amp is rated to 2 ohm stereo. I'm not
sure
what overall affects that can have on the amp... I've done it before and
the
amp would overheat and shut down.

In short, it's not good for the amp if it starts shutting down. Yet he
didn't complain about that happening, so who knows what's going on...