Well couple of things.

You don’t know how long C has been incorrectly yielding. There may well have been enough time for them both to move onward.

Also there’s nothing to say that A isn’t a yet undiscovered C.

I’m from the UK so roundabouts are second nature. I’ve been an accidental C before. Where I had to wait for a lot of cars that had priority over me. When it finally was open for me I was zoned out. Luckily the car behind me was very polite and just used a short beep of the horn to bring me back to reality.