I emailed Walter Block and quoted your question. He emailed a group of Austrian scholars. They came to the conclusion that in the hardback edition there is indeed a typo. They mentioned that it would be corrected in the next printing.
Matthew - ya, I came to that same conclusion since i’ve been continuing my studies. What has helped me to also understand interest is to think of it as the exchange rate between current and future money, as Bob Murphy wrote in Lessons for the young Economist, as well as time preference.