Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
He isn't "some random iOS developer", however. He's a pretty active participant in the Windows beta community, having leaked multiple builds in the past. He's also been a source of some reliable Apple information, usually of which appear on his Twitter account.
 
What points to Thursday? He's Irish so it was actually Thursday when he posted it.
 
Just like I said, some random iOS developer is definitely going to know when Lion betas will appear. Obviously.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.