I went too quick to conclusions, but:
I installed that
soundpack.
I joined Super,CTF server, which from what I believed is a pure server. However I was hearing some of the sounds coming from that pack.
Weirdly enough, most noticeable sound changes were the menu sounds, and change weapon sounds. But the sound pack also contains weapon sounds, and these weren't changed ... !
If server was unpure, I suppose every sound would have been changed.
Now I remind about some issues where loading a mod were a way to bypass some pure check.
I didn't know what was that check removal about and wanted to know, so thanks for the explanation.
Edit: I renamed it to z-dan.pk3 in case it had something to do with its name, but result is the same.