Opportunity cost would be more understandable, although I would agree that it doesn't fit the entirety of that paragraph, but then again neither does "chippy chip chip chop" which is the term I use to describe the same concept.
It's not really opportunity cost because everyone has a different financing structure.
There are people who pay 10% in margin expense and there are others who fund far better than the OCC. We don't know how this guy funds.