As far as I know, sheet music is usually licensed under traditional copyright and remixing/sampling is usually licensed under fairly complicated closed licensing terms, for the cases where samples & remixes are cleared legitimately.

Creative Commons licensing of sheet music & samples would count, but I don't think that's what the parent comment was alluding to - it was a misunderstanding between the concept of "open sourcing" something and the concept of licensing it from the author under more restrictive traditional copyright terms.

Wow, this is a lot less snappy when you have to spell it out.