We can be sure because unless you broke one of the laws of physics and aren't telling me, there's nothing you did that someone else who was swapped didn't do.

[Yeah, that includes dying.]

And look - this might all be new to you, but the rest of us are getting used to this transdimensional crap. His friends might not be comfortable talking to a stranger with their buddy's face, but they'll be able to grasp what's going on.