Viking,
The OP was discussing the service cord wiring, not a service drop from a power breaker panel. Even a panel can use 8 AWG or smaller if the run is 25 feet or less (the 6 AWG presumes a 50 ft run.)
Some RV 50 amp extension cords use even smaller wire sizes as seen here for a 36 ft cord using 10 AWG conductors:
https://www.walmart.com/ip/VEVOR-RV-...yABEgI-TvD_BwE
10 AWG is a bit small for my liking, but it is clearly done for this application space...
Chuck