Afraid you are incorrect about that one, Cardiff never knicked it from Ajax - if anything it was a joint effort.
The first time it was actually sang was at a friendly between Cardiff and Ajax 4 years ago in Cardiff. Ajax never sang that song before at ArenA. There was a bit of tension between the fans during first half and the DJ put the song on at half time and ended up with both sets fans singing.
First home game of the season after that game, VAK 410 Ajax ultras started singing it during the game and by next home game and every game since, it was being played as last song before 2nd half commenced.
A lot better than some of the Dutch pub music played at ArenA before and during games