The bus driver waited for you while you ran. That was a choice, not a schedule.

A schedule gives somebody permission not to wait. Pulling away on time is correct and perfectly defensible, so stopping anyway means a driver decided a kid running down the street mattered more than the clock, knowing nobody would ever thank them for it. That is a small piece of discretion used in your favour. Rules leave more room for kindness than most people take.

Say thank you as you get on, and remember it when you are the one holding a door or a line. Use whatever discretion your own job gives you the way that driver used theirs.