I guess I'm a bit late for this game. I like the idea. It's much easier to tell when some more details are given, but it's not as fun if too much is given. This is just enough info.
I find it's a mixture of B and C, there's also lag involved too. I voted C is the person to blame. B doesn't seem to know C is half a car behind on his left, but C doesn't want to back off. Somehow B isn't being spun and something laggy caused C to spin. C could have backed off to prevent this from happening.