This has nothing to do FR. It was paid for the ticket in EUR and issued a refund in EUR. The conversion profits went to various institutions along the way in the banking system.
Complaints such as yours are common. Not just with air tickets but with other purchases which go sideways. You paid EUR X for the ticket and that is the refund due.
For a piddling sum such as $30, most card issuers will simply eat the dispute, especially when they are not out any hard cash themselves.