When I first read it, I didn't get the impression that the author was implying PG said FB stock wouldn't go up.
In reading the PG post, it seems that a conversation with prominent investor, who was confident that FB's bad stock performance would hurt the IPO, led PG to write a post exploring how that may happen.
In re-reading the NYT blurb, I still don't see it as the author saying PG said the FB stock would not go up but rather as the author believed that PG said that "start-up investments would dry up."
And I think it's in that last sentence, in particular, the third to last word, "would," where the majority of the problem lies.
PG in his post included a tremendous amount of ifs, mays, and qualifying statements talking about how he wasn't sure in which direction it would go. The NYT author, I think, just changed his uncertainty into certainty, both with putting "would" in that last sentence, and removing the "If you haven't raised money yet," part of the quoted link.
So, I see it as the author attributing more certainty to PG than he had in his post, and yet, at the end of the author's post, saying that there is less certainty about this, "The party can’t go on forever, but the infamous question must be asked: Is this time different?"
By you saying, "they're actively misleading," I'm assuming you're attributing malice to the NYT author. I guess I just see journalists and politicians (and many people in general) speaking with an utmost certainty on behalf of people who speak with qualifications and attribute it more to the desire to condense words and present a confident argument than the former. Qualifying statements often use a lot of words. I like to qualify most things that I say and I think journalists and editors often remove them out of seeing them as extraneous—e.g., removing the "I'm assuming", "I guess", "often", "most", and "I think" out of the previous paragraph.