I posted a whole response, but I don't see it... Must have blanked out. But what I said was:
I have honked my horn by accident before. You know, drop something, squirm around to retrieve it, elbow in horn. Don't assume it was at you!
And, I have honked my horn for no reason before, like if the kids are in the car and we are singing along to the radio...
I came back to say, even if it was at you, it was probably just in annoyance of having to stop at a light with no cars around. Their problem, not yours.
In other words, don't internalize this. It really had nothing to do with you...