Exactly, it's mPCIe only and that's the reason you can add 2 more SATA ports for less than $15 as explained above: http://forum.banana-pi.org/t/banana-pi-bpi-r2-open-source-smart-router-with-mtk-7623n-design/2697/31?u=charles
I think with the Clearfogs you can switch between mSATA and mPCIe while on EspressoBin it's PCIe only. No idea.
But since it's PCIe you could even add real PCIe cards with 4 or even more SATA/SAS ports with something like this: https://www.aliexpress.com/store/product/PCI-express-to-Mini-PCIe-expension-adapter-PCI-e-x1-to-mPCIe-card-supports-Sound-Card/909573_32780634356.html (not that useful when just a single PCIe lane is available 
)