I don't know about where they are but around here (the Northeast US) honking for a bride and groom is kind of a traditional thing to do. Except usually they're getting into a car not a carriage. Anyway, you might be right but I think it's just as likely that the honker was honking because "wedding" and was just too dumb to think things through to their logical conclusion.
I got married on the Brooklyn Bridge. The cars driving below us started honking in a unison (HONK pause HONK pause HONK pause) to distinguish the celebratory noise from the general traffic din.