Trusting players to keep a big juicy piece of news secret is nothing short of a fairy tale!
Murphy's caution was really just part of the NPC's routine, reinforcing his character. By his guess, within about ten minutes this news would be the talk of the forum. Yet, he couldn't care less, in fact, he was looking forward to it.
A good game needs to occasionally create some buzz, not only to strengthen the engagement of current players but also to attract external attention.
Of course, Murphy's situation with "Real Different World" is somewhat special. It doesn't need much external promotion, but as a forum admin, it's his duty to maintain a good community atmosphere.
Currently, there are only about 60 players who have received beta test invite codes on the forum, but Murphy has already approved quite a lot of applications.