What wasn't understood then, and still isn't really understood today, is that the reality of money is of the same type as the reality of centimeters, grams, hours, or lines of longitude. Money is a way of measuring wealth but is not wealth in itself. A chest of gold coins or a fat wallet of bills is of no use whatsoever to a wrecked sailor alone on a raft. He needs real wealth, in the form of a fish rod, a compass, an outboard motor with gas, and a female companion.
But, everybody else besides the shipwrecked sailor who had the coins or wallet could just buy those things... so what is this guy's point? When one measures those other things, they don't change based on your circumstance, a meter is still a meter, in LA or on an island. Just way off base this guy. (Maybe that is why it isn't understood.)