Well then, don't ask him in an accusatory way. Ask him out of curiosity. Not distrusting, just wanting to know what part of his build did that (because you've obviously never heard of it before).
I mean, you might want to use it yourself sometime.
And heck, even I'm curious at this point. There IS some vague memory I have of a feat or something that does that, but I can't remember or find it.