Yeah, you have to be able to mount your motherboard on the other side of your case and flip the back panel so that the I/O panel and slot openings line up.
My case just happens to be both ATX and BTX compatibility and after doing a bit of reading and talking to a few people I decided to use the BTX fashion instead. It was also better for the window and side panel blowhole positioning.
If you were to flip your board and try and mount it on the right side of your case, obviously the slots would literally be inside the case pointed towards your drives
I actually made a post on this a while ago back when I was still decided but no one took note of it