Having to assume a non-zero possibility that anyone you interact with on HN is secretly Zuckerberg makes the whole experience just that extra little bit spicy, doesn't it
I think the connotations of "spicy" include danger, thrill seeking, and titillation. Whether that's "good" depends on your personal appetite for such things.
you could be excited by the (idea | risk) of Zuckerberg reading you writing bad things about Zuckerberg or Facebook, or saying these things to him without knowing. Like a game. This is how I understood the post and it matches your interpretation of spicy.
Posting on twitter secretly doesn't make sense unless you have good followers. Obviously you can do that for friends and family but com'on twitter is not for friends and family.