I think his rude comment stemmed from exactly what he said.. that you just wanted to check up on them. In this scenario, I can understand his frustration if he truly has no interest in this woman.

Yes, it was rude. I also think he's tired of the questioning.. and as I've said already, he's dug a hole for himself because now, even if he's telling you the truth, you're not confident in him. He's lost credibility. Too bad for him, though.. he needs to take this piece as part of the puzzle, due to his own actions.