For the record, the only other "pure" Frenchman to have played in the NRL was Jerome Guisset, who made 4 appearances in the forwards for the Canberra Raiders in 1999, at age 21. He had previously played in the Canberra Raiders junior setup. (Later he joined Warrington Wolves in Super League where he made 138 appearances 2000-2004, Wigan where he made 22 appearances in 2005, and Catalans where he made 141 appearances 2006-2010). Guisset who played second row and later mostly prop, never scored a try in Australia (though he scored 39 with Super League clubs). Guisset has represented France but is now retired as a player and is assistant coach at Catalans.
Benjamin Garcia, a second row forward from the Vaucluse region in France came to Australia in 2013 at age 20, and played in the Brisbane Broncos Under 20s, but never played NRL. In late 2013 he was signed by Catalans, where he is a second choice back rower.
Jason Baitieri, born in Paris in 1989 to a French mother and an Australian father (former player and coach, and currently RLIF official Tas Baitieri), is a lock forward who played one game for the Sydney Roosters in 2010. He was then invited by Trent Robinson to France where he signed a contract to play with Catalans Dragons, (for whom he has made 84 appearances and scored 13 tries) in Super League (Europe). Jason Baitieri is in essence binational -- a citizen of France and Australia.
So Remi Casty is not the first Frenchman to have played in the NRL, but he is the first to have scored a try in the NRL and, barring serious injury, he is likely to become the longest serving French player in the NRL -- perhaps as soon as two weeks from now.