Terrific find - what a shame it was France. These will be cleaned, cataloged and then left to rot in some museum warehouse. The poor property owner is no doubt not happy because his expansion plans will have to put off for years at least while the archeologists do their "work." And of course even though the coins were found on his land, he won't make a dime from the discovery.
It's true that in France a property owner is not the owner of historical objects found in his property. If you dig out gold ingots in your own garden they are yours, no problem, but if it's a hoard of Celtic, Roman or medieval coins, it's national heritage. You cannot oppose the state seizing it to be studied by numismatists. And even after it is published, it will not be returned to you but secured for future generations. Technology evolves and an ancient coin hoard published in the 19th c. may be republished today with modern standards and analyses. In France and some other countries, History is not a merchandise that can be sold for a private financial profit. It's our common History.
