Not defending the use of wood in this example since none of us know the story behind the reason for his making a receiver out of wood in the first place.
For all we know he may have been towing some little 4x6 trailer with a push lawnmower loaded in it, in which case the hitch would have been more than sufficient
We need to remember also that back in the day wagons were made almost entirely out of wood even having wooden beams for the axles with only an iron stub for a spindle these wagons were sometimes made to haul tons of ore 100s of miles pulled by huge teams of draft animals.
Even the early heavy duty trucks had wood frames and they hauled tens of tons over less than perfect roads sometimes without roads at all