John S.
On further thought, I think you’re probably right. There was a brake rider, but they were distracted or possibly the brake/hyd accumulators were not charged, assuming the APU wasn’t running. Years ago, I had a tow bar break while riding brakes on a USAir DC-9 and it took a moment to realize the tug was driving away from us.
Rob S.
You don’t have to have the APU running if the brakes/hyd accumulators are charged. But it’s best to have the APU running if it’s practical.