mATX boards are basically half sized boards compared to standard ATX. The Silverstone case you linked is made for mATX boards this size. mATX cases are made with only 4 or 5 PCI slots for expansion slots. That makes it easier to visualize compared to the 7-9 PCI slots on mid tower ATX cases.
It says it can support mITX boards because it can.
mITX boards are tiny. Look at how small they are compared to the bigger boards. All 3 cases I previously linked will house the mITX board and parts you linked comfortably. Just know that mITX boards only have one PCI-E slot and that's it. They have limited I/O due to their size. That eVGA Hadron case even comes with a PSU so you wouldn't have to buy that. BUT they will not support that cooler you have linked. You'll need an AIO water cooler or a low profile air cooler.
Most mITX cases are small and portable. That's the whole point of miTX. If you decide you want that Silverstone case instead, just get one of the mATX ASRock boards mentioned previously (the H81 or M97). On that note, if you want the Silverstone case for expansion or upgrades later, might as well get the 200r. The 200r is small enough I can fit under my arm and carry it one armed around. If you're that serious about moving it about I suggest getting yourself a case carrier like I have.
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