That's a crappy law if it applies to sales to non-coercers. It would have the effect of discouraging folks in a position to help future persecutees if they could be forced to refund compensation for efforts made and risks taken.
In any case, the court's decision states that, facts aside, they don't believe the 1998 law creates a private cause of action.
The determination of coersion is based on the statue of the seller A Jew in post 1933 denied citizenship, denied employment in many venues, some property already formally confiscated, other like artwork, jewelry and financial assets not able to be transfered to heirs, rather reverthing to the state, limited freedom of movement. Under these circumstances, transfers have been deemed by several dozen countries to have been coerced.