Hm... I don't really understand logictheo's reasoning, and he points to a link that is dead. There's one archive of that page on archive.org,[0] and I don't see any information about that (note: the style is all messed up, it's black text over a black background). The page referenced in the first post of that thread is also dead, and not archived by archive.org.

I did a search on STK's bug tracker, and although nobody has reported any music as being wrongly licensed, I did find this bug report that mentioned Speedsound's music.[1] It suggests that the music from Speedsound is taken from an old album that was licensed under CC BY-SA, and it's the newer albums that are under a different license (CC BY-NC-SA). It also suggests that Speedsound stopped distributing this old music under CC BY-SA, but that would not void a previously existing license grant.

logictheo doesn't even say explicitly that he knows this particular piece is not really under the license the STK developers say it's under. He just says that it's "by this [same] artist but in another album" and seems to just infer that it must be a mistake. He doesn't even seem to try to prove this, it's just speculation.

In any case, I've opened a ticket on the STK bugtracker.[2]

[0] http://web.archive.org/web/20120728083029/http://speedsoundrec.com/aboutus/

[1] http://sourceforge.net/apps/trac/supertuxkart/ticket/685

[2] https://sourceforge.net/apps/trac/supertuxkart/ticket/1048

Links above to STK bugs are broken; here is where they moved to:

https://github.com/supertuxkart/stk-code/issues/741

https://github.com/supertuxkart/stk-code/issues/1104