Originally Freestyle Chess referred to something else entirely, namely “anything goes” online chess: https://en.chessbase.com/post/scintillating-che-in-the-pal-c...

You were allowed to use engines, opening books and tablebases. You were allowed to play in teams (GMs were part of some). You were even allowed to bribe your opponents into losing! But it died out fairly quickly and now the name has been reused to mean Chess960.