Vapour lock is where bubbles occur in the fuel lines or anywhere else in the induction system. The usual place is in the line between the fuel pump and carb but it can often occur in the carb itself. Like you say it's due to the slightly lower boiling point of mogas to avgas. A return line from the carb to the tank is sometimes used to help evacuate any vapour created this way. So, what you describe is classic vapour lock ... I used to get it a lot in an old Volvo I had too. I wasn't really being sarcastic .......
OK maybe I was, but it was intended to be humourous ... I'm often the butt of a joke or two but I've learned to lighten up
IM
I'm sure someone more techie could give us a proper definition.