Well that's interesting. I wonder if that's for Early Access usage only, so that people don't go overboard on Netflix/YouTube which apparently currently works over LTE, or if it's meant to be for Premium Interiors on a per-month basis, for the same reason. In that case you'd expect to see a date range to keep track.
It will be just wifi once it is rolled out to all. Elon has stated that he wants to start installing wifi at supercharger locations, but for the early access program you can use cellular to test out the software.