Can high audio input level cause video loss or video distortion in camcorder?
The only thing I can imagine is that this guy had a bad experience a long time ago with an analog tape based camcorder. I could conceive of a situation in which a badly-designed unit would allow an excessively hot signal from the audio track to bleed over into the adjacent sync track. Any decent unit would have been designed to limit the audio level before this could possibly happen.

I assume your modern camcorder is both digital and uses solid-state storage. In which case, there is no possible way for the audio signal to affect the video (or vice-versa).