Assuming the story is true, I think he just said this because he was embarassed by it. Mesereau admitted it was Michael's porn, and they were found in places where they couldn't be anybody else's (like underneath his bed or in his nightstand), so case closed about that one. And no, it doesn't make sense either that the defense would plant something like that to make him look straight, or something. Michael didn't expect the raid. When he heard the news while he was in Las Vegas, he was so upset that he trashed his hotel room (
http://www.contactmusic.com/news.ns...-hotel-room-as-police-raided-his-home_1116386 ). I could go on about why these mags weren't plants but I will stop here because it's not the thread for this. I will say though that the defense fought AGAINST these magazines to be introduced to the court and it was the prosecution which wanted to present them to the jury so bad, so again it doesn't make sense the defense planted them. The prosecution eventually got their way in showing them in court, but nobody really understood what was the point - probably to try and prejudice the jury against Michael, since they had no real evidence against him.
So the reason why Michael was embarassed by this fan's question is probably because he was reminded how Sneddon tried to humiliate him. This quote is from Taraborelli and here is how he remembers those days inside the courtroom:
"The worst week was the one we members of the press privately called ‘Porn Week’. Day after day, the prosecution showed, on an enormous screen, graphic pornographic images from stacks of magazines found at Neverland. It was awful. I remember sitting watching Michael’s poor mother Katherine as she was forced to look at those photos. None of it was gay porn. None of it was kiddie porn. So why show it? The prosecution suggested that it was straight porn used by Michael to turn on straight kids and encourage them to then have sex with him. It didn’t make sense to me. One magazine, maybe. Two? Maybe. But stacks and stacks?"
It's one thing to have porn at home and watch it in the privacy of your room. But it's a whole another issue when it's used against you just to humiliate you. That's what happened to Michael and that's why he didn't find this question about girlie magazines amusing.