I think customer speeds is 144 and the 6Tb is their ground links to their stations. That is my take on it at least as its not super clear. I'm curious as to how it works as well.

My read was that they're going to have 144 Gbps RF for both regular users and their ground station gateways, and 6 Tbps optical for satellite-satellite back haul, but then you can also buy direct ground-MEO access to a back haul link. (Presumably MEO-only because it's hard to maintain the link to a fast-moving LEO satellite?)

They don't seem to mention using optical for their own ground stations - maybe too unreliable?