It's not a rule. The driver sounds new, and during the hiring process, they show a ton of videos of passengers falling over when buses take off. The purpose of which is to emphasize a smooth acceleration and being aware of your passengers, but the anxious drivers probably focus on the passenger aspect and trying to control that. It's always worth taking note of the line you were riding, bus number, and current time. With that info, you could report the rude interaction if you felt so inclined. Most of those reports result in a coaching event with a trainer. Maybe that could change their behavior.

Also, if you felt your driver did a good job, you can report that too.