"Forgery" would mean he made it himself. He was accused of passing a forgery, knowingly or unknowingly. Most people don't even look at their change, they just spend it at the next place.
According to August 2019 article, the U.S. Secret Service is working with [Minnesota] retailers to stop the flow of counterfeit money coming into the Twin Cities. If cashiers, who work with money all day long, need education to spot fake notes why should anyone expect that a regular citizen would recognize it? I have the skills to detect counterfeit currency, but since the pandemic I have been touching the bills I receive as little as possible. https://minnesota.cbslocal.com/2019/08/13/trying-to-be-very-aware-twin-cities-retailers-on-lookout-for-counterfeit-cash/
Here is a January story on $900,000 of counterfeit US currency seized by Customs and Border Patrol in Minnsota. https://www.kare11.com/article/news/local/counterfeit-bills-seized-at-minnesota-border-international-falls-china/89-920a8623-b78c-4d52-a735-6eb913ffd98d