Wiring the center out of phase causes a very small imaging effect. If you're sitting in the sweet spot and move left and right, the center channel image might move left and right more dramatically than it should. The key point about this is that the center channel, out of phase, only causes problems in audio that can be heard.
His problem is not that.
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
