1. Fast charging has not been enabled by Apple iOS firmware as of yet, it is rumored to be included in the next release.
2. The two wireless chargers in the Apple stores from Mophie and Belkin have passed Apple's screening and are guaranteed to fast charge when Apple releases the aforementioned iOS update.
That's all we know.
My theory is that besides getting behind two of their largest accessory partners with healthy orders Apple is also concerned about the 100s of third-party wireless chargers that claim fast charging but will not actually fast charge with iPhone 8/X because they either are a) designed for fast charging at a different wattage or b) can fast charge at the right wattage but only using the right USB power supply and almost none of these come with a USB power supply.
I don't think it's coincidence that both the Mophie and the Belkin available at Apple come bundled with their own power supply and don't work with USB adapters. It's the only way to guarantee that consumers won't use a crappy cable or an under-powered adapter.
I myself was recently fooled on Amazon, bought a third-party wireless charger for the kitchen only to find out upon speaking to customer service that it will never be able to fast charge with Apple devices and I'm even having problems getting it to slow charge my iPhone X via a USB adapter I already own.
So it's good that you have the Mophie as it's guaranteed to work and it's a great product (I bought one with my X, love it). But it's not capable of fast charging until iOS 11 is updated again.