I am not an expert or even hobbyist in paper finance, but the author did address your point, a few sentences later: "JP Morgan can't create reserves, it can only borrow or buy them."

I believe the implication is that investment banks can not perform certain actions with their own money due to 2008-2010 reforms: for instance the Volker rule https://www.investopedia.com/terms/v/volcker-rule.asp