The car's on-board processor has enough logic to follow the track lines hidden under the track surface. The BTLE connection to the car is used to control speed, change lanes, and trigger lights. It also is used to 'drive' the car in some cases if needed.
Interesting, our experience was exactly the opposite. I got the kids a set for Christmas (maybe 2016?), and I don't think we ever got it to do anything interesting. I could never tell if it was charging, phone, app, interference, or something else related. Maybe we just got a dud.