Honestly I browsed through her post history a bit on Smogon and they seemed like a pretty well-liked and honest sounding person, so I kind of thought they wouldn't risk their account by making stuff up. I hope it's real now too since I made the thread and all haha, plus I legitimately love those Starters.
As a frequent poster on Smogon and from my personal experience with her, I highly, highly doubt Cresselia~ would lie about anything related to this. There really isn't a benefit on Smogon for doing that. I guess it'd grant her notoriety outside of the site, but she legit seemed worried about her "smogon reputation" being dragged through the mud if this turns out false, which I doubt would happen lol.
In fact she seems pretty unsure about the rumor at the moment, mainly because she thinks the idea of a Pokemon game without gym leaders to be pretty crazy! She just shared this because the rumor may have predicted Salandit is all.
I should also note that the Orange Islands part of Smogon (that's basically the only forum where you get Pokemon discussion that isn't in a competitive context) tends to be pretty strict when it comes to discussion about rumors. People who spread rumors don't necessarily get banned, but discussion about them gets shut down pretty fast, to the point where the Sun and Moon thread gets locked once there's nothing to really talk about. The fact that they're having a "free-for-all weekend" over a rumor is very unusual to say the least!
Of course, this all could be hogwash in the end. But if it is, please don't claim that Cresselia~ made it all up, because honestly, this blew up way beyond her expectations when she just wanted to share something interesting she heard about with Smogoners.