OK, I've thought further. When a close call happens, I try to evaluate the part I played in it and ask if I can do better.

I rarely listen to music on the bike, but at that moment, I was listening to music. Did it cause me to be less aware? It's hard to say for sure, but maybe, and that's enough of a warning to me.

A cycling friend suggested that making a signal of any kind to let a driver know I heard the honk can help, so I'll do that more often than I've been doing.