From the study...

>When merchants raise prices for all consumers in response to these costs, users of low-cost payment methods (e.g., cash and debit) cross-subsidize high-reward credit card users who shop at the same merchant"

Cash handling is not a low-cost payment method, Cash handling can cost businesses between 4% and 15% of each transaction, when factoring in labor, security, bank fees, and risks like theft and counterfeit bills.

One could argue that credit card users have been lowering prices for cash payers as business avoid cash handling pitfalls and get their funds safer and faster.