You said "usury", which is a word that describes loaning money at an exorbitant interest rate. So it's no surprise GP thought you were talking about interest rates.
(Yes, I know "usury" has had other meanings, but this is the current, common definition, and if you're going to use a word in a way that's uncommon, you should be prepared for confusion.)
(Yes, I know "usury" has had other meanings, but this is the current, common definition, and if you're going to use a word in a way that's uncommon, you should be prepared for confusion.)