I think your instincts are dead-on. Unless your friend is widely hailed as the town's biggest skank, his level of suspicion is unwarranted, and probably speaks to at least moderate anger management problems and/or excessive tool-ness.

As to whether you should get into the middle of it, that's a very different question. Let me answer it with a question of my own: in the movie Armageddon, would you be Bruce Willis, or Ben Affleck? Are you the dashing hero who gets the girl, or the gritty realist who does the right thing, even if it means getting bombed into space powder.

Because odds are, if you just didn't get involved, your friend would eventually come to you for support about some douchey thing this guy does, and you'll have your in. But, that entails knowingly let her endure doucheyness.

On the other hand, intervening now, when she's clearly feeling the full effects of love radiation, may cause her to distance herself from you or get angry, damaging the friendship (and maybe even driving her further into the arms of Big Brother).

It's a tough call, but I wish you luck. And if you're looking for a wild card option, may I suggest carrying around a series of photographic backdrops, so the next time the guy asks for a cell phone photo verifying her location she can say Irkutsk or Narnia?

If he can't take the joke, he's definitely a pass.