It has to. 135W power supply for a device which is 8.5x8.5x2.3"
There's no way that much heat is going to be quietly removed by those tiny fans.
I'd love some high res photos of the inside so I could look up the data sheet of the fans in use.
Considering HP servers ship with cooling ducts to direct airflow and this thing doesn't even seem to have them. I mean look at the CPU exhaust! From the photos it looks like the only vents are at the corners, but they've decided to exhaust the CPU (and presumably the GPU, hard to tell since it's under a hard drive) straight into the rear IO ports which don't have any vents to the outside.
I'm not aware of PC manufacturers making a SFF PC with an internal power supply (look at the Dell Optiplex GX620, and Steam machine).
Pretty much any PC small enough to be VESA mountable will have an external power supply.
Apple has made the power supply on the Mac Mini internal since 2010, but previous models had an external power supply. I can't find exact numbers, but I'd be very surprised if the power supply in the current Mac Mini model is rated for more than 60 or 80W output.
But besides, it doesn't really matter if the power supply is internal or external, other than it would be a feat of engineering to fit a 135W power supply and a PC in such a small space. The fact is, that volume is quite small to fit the components and a heat sink which can handle a 60-80W TDP (CPU+GPU) without having a lot of airflow over it to keep temperatures under control.
