It's hard to imagine that a rail system would try to preserve cheaper fares for locals in this way. It would be far easier to just give then a discount based on residence. However, I don't know so I can only guess.
In any event, someone should point FIA to this and encourage them to follow-up. If their cards do not work, while other US issued cards do, I would think that would be of concern to them.
BTW, I have found in every case I have tried that buying tickets from the local rail company was never more expensive than Rail Europe and is often cheaper, sometimes dramatically so.