This is the twitter post?
https://twitter.com/bfdradio/status/976856668440064005
What you have here is a JPS NXU-2A NEU/RoIP gateway. It's usually used with things like the ACU gateways for patching.
That's basically it. Instead of patching this half-duplex LMR RF link by copper or RoIP over ethernet/fiber, it is linked, or "backhauled", by wireless.
FirstNet: for the time being, you can think of it as a cellular provider - because that's what it really is. It is AT&T building out a cellular network using dedicated band 14 700 MHz spectrum (20 MHz of it), meant only for public safety use.
Funny enough, in this picture, nothing is actually working. The NXU isn't connected, and the Cradlepoint COR IBR1100 above the NXU only has WiFi connected - no cellular. There is no FirstNet running in this picture.