I am pretty sure there are several typos on Danny's part because that quote does not make any sense. A full C rate discharge basically means he is emptying the battery at 40C x capacity (remember, capacity has a time component to it). And then he says once this is completed, there is still 90% capacity!
I agree that we cannot trust the C rating from different manufacturers though. They all come up with their # a different way. I thought C rating was derived by drawing the max amount of current until full discharge and the battery never reached its cutoff voltage.