I'm not trying to say the bus driver wasn't in the wrong, I've had plenty of encounters with very bad school bus drivers. It's a part time job with low pay at least in my area, it's not a job that attracts more qualified drivers with a lot of experience.
They'll have those convex mirrors too. What I'm saying is if the traffic wasn't congested and the driver of the car was loitering in that area going the same speed they contributed to the accident.
When you're driving in a truck you're constantly checking those mirrors and movement in them, you need to be aware of the traffic around you. What happens if someone is traveling in that area for a while you might lose track of them. You don't see any movement in the mirrors for a long time and you get the sense no one is there. You don't see anyone in the large mirror and if you don't check convex mirror you'll never know they are there. I've had this happen to me plenty of times only to find out there is a car next to me when I looked in convex mirror.