You misunderstand. That's alright, he came up with a pretty revolutionary (I think) concept.
The idea is to use the traditional PC case as an external PCIe solution through Thunderbolt. So the Eve would be the computer, but the box would offer the ports that you'd traditionally find on a motherboard such as a PCIe16x slot for a graphics- or other expansion card, M.2 or SATA ports, and USB- and Ethernet ports.
This board could be the core of someone's external hard disk array. It could be the core of someone's eGPU box. It could be the way to connect a pro audio sound card, or a video capture board, or a variety of things. By being mITX compliant, people can choose their own off-the-shelf case and power supply based on what they need to add over TB3.
It's not likely to come into existence, but it'd be a very cool product indeed!