I'm not sure it's so much "fake" (though it could be) as "really really super-duper early." The leaker mentions this is info from the 1.0 version, and they're on 1.5-ish by the time of his post. It sounds like a lot of it was derived from earlier books, just pasted all together and given out to people for the first early round of testing.
While true, here's my problem.
v1.0 leak - "Oh it's just super early. Nothing is set in stone."
Internal alpha test - "Ok, so it's still mostly bad, but internal playtesting will fix it."
Beta test - "So the design philosophy hasn't changed at all yet. Don't worry. They'll surely listen to everyone who hates it and make the needed changes."
Release - "So they only tweaked the numbers on some stuff. It's only the first printing. We've still got errata and splat books to look forward too."
We've all seen this happen before. WotC did it with 4e. Paizo did it with Pathfinder. Once a dev team gets going down a specific design path, they aren't going to drastically change it. To do so costs lots of time and money. It's also really bad to tell your investors and your CEO that everything you've done up until now has been a waste and needs to be redone.
The incentive then is to only listen to feedback that falls into the chosen design philosophy. Any criticism that does not follow the chosen core design, or criticizes the core design, no matter how insightful or constructive it may be, falls onto deaf ears and is disregarded.
This leak gives insight into the chosen design philosophy of 5e. We now know that it is geared strongly towards winning back members of the OSR and Pathfinder crowd with a steep 3.5 angle, and traces of 4e are to be cut and minimized wherever possible. I do not see this core ideal changing radically for the final product.