I seriously doubt brakes, whether on the plane train or a real plane, would produce enough smoke to be visible from the rental car facility.
A couple of years ago I checked into the E skyclub and noticed a lot of black smoke around the south cargo ramp, the desk agent said they were doing "firefighting practice."
When doing live fire training at the fire training center, there will be a lot of black smoke.
FTC | ATL | Hartsfield-Jackson Atlanta International Airport