I've been asked to do this for a friend. I can pretty much figure it all out aside from the outside edge; the fluted/rippled part. It looks like it was put on at the end, rather than poured at the same time as the top. But what on Earth?? I'm no expert by any means so perhaps it's something easy.... but you all are so great at these things I wanted to check with you first... before I tell her I can do it.
they probably use a mold since this is a mass produced item by a big company. you can use a giant cupcake pan (like the ones on the infomercials) to make a shell like this, but it would probably not be wide enough, and would be too tall.
The one in your link does look like the exterior is a separate piece (or pieces, connected)...maybe it's modeling chocolate...I think you would be able to make that fan-fold with rolled out modeling choc. as jgifford said.
There are instructions some where on this site for making a chocolate mold for the large cupcake pans. It would be the same principle. The cake layers are placed into the chocolate mold, filling layered in, next cake layer then topped with a ganache the same colour as the chocolate mold.
Hope that helps. Good Luck. Looks yummy! My son would love it!
I think the best way without having to spend a bunch of money would be to make chocolate panels, and put them together around the cake to get the shape you're looking for. There should be plenty of tutorials out there on how to make chocolate panels.