Checkout his homepage it's full of embellishment, so he doesn't believe in what he is saying, it's just currently the trendy thing to say and hasn't had time to redesign his homepage to fit in what he's is preaching.
You're right. I checked out his homepage and it seemed like the opposite of what he was saying in his post (irony). But I think he made some good points nonetheless. Not necessarily that "flat design" is good design, but that Design's goal should be to enhance the communication of the content and not distract from it.