I think this is a bad idea. There is much potential for user irritation if they're trying to read or click on the top part and it scrolls away. It's unconventional and unexpected behavior that will make people stop and think, which is generally frowned upon in this business. A worse case is if users happen to be looking away and not notice that it has scrolled down and have to find the menu (hopefully) by exploration.
My guess is the majority of users will actually scroll back up to see what they've missed, making that initial scroll down somewhat pointless.
From a design perspective, that whole page filling header could tightened up, made smaller with less white space, and still be aesthetically pleasing, allowing more of the real content to be shown on page load, negating the need for this initial auto scroll down.