This is a site guideline I fervently disagree with. Throwaways with no reputation to back them up should be treated as irrelevant - they don't face any social costs and indeed they accomplish their goal almost immediately and there is no mechanism, none whatsoever, to undo their damage.
The problem is the fundamental information disparity. The guidelines want us to treat anonymous astroturfers with the same deference we treat "a source familiar with the matter" as reported by a national news publication. There's a difference though: journalists ostensibly act as a filter and a guard against bad faith[1] use of on background or off the record conversations, and try to fact check or cross reference those statements. And journalists usually know who their sources are, and statements in error can result in that source no longer being valued or used.
Hacker News as a discussion site has none of that. We have no way to know if this person actually works at Facebook, actually conveys true information about Facebook, and if it turns out 6 months from now that they're an astroturfing troll or PR firm, the damage is already done. Disinformation online works so well because the initial comment, like this one, gets so much traction and it's unlikely any retraction - if it ever comes - reaches the same audience and causes a reversion of their prior beliefs.
I think it's very silly that the policies ensure the site is exceptionally vulnerable to disinformation campaigns, and too many people presume good faith in an age of anonymous online bad faith discourse.
[1] - let's not wade into the current dialectic, but this is the ostensible purpose of journalists knowing sources, but not divulging them