NAGPRA the federal law is probably what you’re thinking of. It was implemented because some jagoff decided to sell gravesites off his property for people to dig up for fun. If your friend has gravesites on his property he would run fowl of the law.
Artifacts such as what you have are private property. Responsible owners might alert an archeology department that he has a site on his property. I worked on a dig that was on a farm in Ohio. There were no graves. The site was dated to about 1000ya and was a Woodland period site. The farmer liked learning about the previous inhabitants.
“fowl” or even foul
Wasn’t me.
I ain’t got nuthin.
This is a total fiction.