> If you wish to use my music for commercial purposes (online advertisements, podcasts etc), you will need to purchase a license

This clearly makes it not CC-BY. Maybe CC BY NC?

IANAL but I think legally, if you put CC-BY on it, then just write in the comments that you can't use it commercially, that wouldn't stand. CC-BY-NC is available, and the author did not have to upload it as CC-BY in the first place.

To be clear, I still think this site has some problems, and author's wishes should be respected, but I think if the author wants you to not use it commercially, they should put the correct license on their work.

It's neither. You can't just match up the terms of Creative Commons licenses then assume because they are similar that you can say it's Creative Commons licensed.

Go Check the soundcloud link of the title and tell me what licence CC you see!

It is unclear what the actual license for the track is when the author says very clearly states that commercial use is restricted, but the author also selected CC BY 3.0.

These two things are in conflict with each other, so it probably makes sense to chose the most restrictive option.