It's a common metaphor.
There is also a risk measure explicitly based on this concept:
https://en.m.wikipedia.org/wiki/Bus_factor
But I guess that there are not that many buses there in US so a car crash may be more appropriate.
The metaphor is perfectly unnoticeable in everyday contexts, but in his state, careless edges of arguments must feel awfully pointy.
I learned that the hard way when trying to support a friend down on his luck.