The combination of the dirt, the mice, and everything sounds like nutty homeopathy-style theories for dogs to me. I'm honestly a fan of some of the hippie nonsense that's better supported (e.g. raw feeding, not feeding cats a bunch of grains) and don't see any issue with feeding frozen mice to a dog. It's healthier for them than a whole lot of stuff that dogs commonly get fed. But then there's the people with really weird, clearly wrong ideas like vegan cats or at a less nutty degree but similarly harmful, any raw feeding is better for dogs/cats so let's throw some meat in a bowl and call it good until the cat goes blind from lack of taurine.
Closest I could find - but this holistic dog website advocated "soil based organisms" for dogs. That could easily be morphed into "feed them some dirt."
https://thewholedog.com/soil-based-o...sbos-for-pets/
Sooo if this is what's actually happening...I have a feeling you're not going to be able to convince them of anything at all. People who are just doing things for convenience don't really go to the effort of getting mice and bags of dirt so I feel like that's not it.
You can see what you can convince them of, but if not, you might have to just keep an eye on it and see if it gets bad enough to report as abuse.