Car stalled while pumping gas

Sure it could have been vapor lock. Sitting at idle on a hot day could do that. They do make kits for adding a return line for classic or muscle cars running mechanical fuel pumps that will prevent vapor lock.

For your own safety and those around you at the pump, do not fuel the vehicle while it is running. Fuel vapors spread from the gas inlet and could easily be ignited by a hot exhaust component or electrical spark.