I just looked at it for the first time. It looks a little amateurish (what, no search bar?), but I don't see anything suspicious. This dude is charging 15 bucks for the convenience of compiling his collection of digitally recorded public domain music which would otherwise be free. If you want to pay him 15 greenbacks, okay.
If it were a scam, I do not see how it would work. I suppose he could offer copyrighted music and pass it off as PD, but it wouldn't be worth the risk nor effort to him when he can get the genuine stuff for free just as easily.
The site does look legit to me. Don't take my word for it. Think of a few PD tunes and search his collection to see if they are on the list. Keep in mind that copyrights expire later in the U.S. than the rest of the world. Search for "In the Hall of the Mountain King" a classical composition and "A Podsafe Christmas Song" by Jonathon Coulton.