Here's the Readers' digest version
The government made some 1933 $20 gold pieces. Thanks to FDR, they were never issued, then melted. This family got their mitts on some, anyway, so yes, stolen, or illegally obtained.
BUT
There's a long history of rarities being illegally made, think the 1913 Liberty Head nickel to name one. What makes this case unique is that the government is actually going after these.
Interesting test case, with what will probably be implications for other illegally made/sold stuff.