The statement comes in the form of a message board post by Chet Faliszek, one of the writers on Half-Life 2 and Left 4 Dead. He sounds a little disappointed that fans are taking the fake promo so seriously, even going so far as to outright say that they're all being trolled something fierce. None of the supposed teasers have come from anywhere near Valve, and Gabe Newman certainly hasn't authorized any leaks from the near future.
A statement like this suggests that Valve isn't actually anywhere near completing the third episode in the Half-Life 2 storyline. If they were, even the fake viral marketing would be good for them (hey, free press). As it stands, it seems like episode three is on the back burner, much to the chagrin of devotees everywhere, I'm sure.