Yeah, that's what I was thinking too. If you look at the full description, it says "We offer the next generation of high speed storage support through M.2 and SATA Express. M.2 and SATA Express transfer data through a PCI Express 2.0 x2 interface up to 10 Gb/s, making it 67% faster than SATA 3.0 solutions." However, right from the start, and several times in the manual, it says it offers Turbo M.2 to run it at 3.0 x4.
So either there's a setting somewhere, or there's misinformation. I bought this board specifically to run M2 @ 3.0 x4.