Let's assume for the sake of argument Pokebeach is wrong about Dual Type moves, and Freeze Dry (and possibly other unconfirmed brethren) is the truth behind the scenario...
...doesn't this just further he's right despite being wrong?
What I mean is that, again, he's clearly not full of crap. The situation would be simply explained by he used an attack, it worked different than the expected outcome (Ice being SE vs. Water instead of NVE), and assumed "oh, maybe moves can have dual typing now!"
IOWs, a simple mistake, or he just got his facts tied up or whatever. These things happen; basic human error. If Freeze Dry is indeed what he was referring to, then it doesn't mean he was full of crap; it just means he is fallible.
He did, afterall, already get the Fairy type rumor slightly botched. Why were people willing to dismiss that? Because everything else he said about Fairy was true, its easy t just assume that he remembered wrong, had a legitimate typo, thought one thing typed another, whatever.
He simply botched the info. This is different than a leak that appears, says a whole bunch of things, and then is proven wrong on the first new detail we learn. In that case, the guy was clearly full of ****, and we ignore the rest of the leak.
In Pokebeach's case? After getting so much right, he finally gets one or two things wrong, and they are explained by basic human error...yeah, I'm still willing to trust the leak, as even if he's wrong, there's likely some reason behind it. --- www.rpgdl.com The site Meeple argues at for too much of his life!
I don't think anyone is doubting the leak anymore. It's more like people trying to explain a possible honest mistake on the part of the leaker (who is not WPM himself, he just posted it in his site), or a detail that got changed.
All in all, I don't think Freeze Dry is a dual type move, but a move with a very specific effect. Sort of what Psyshock and Psystrike do, like it's already been said.