Now does the guy who found it get to keep it and sell it to the government, or do they just take it from him?
As it was a buried stash its trove which means the government gets it by law but has to pay their idea of market value to the finder and landowner.
To get around this (if you are so inclined) the best way is to "find" it again in a location that won't be covered by treasure trove restrictions, like a river or the sea, but check no one owns the particular riverbed or the seabed first.