Music Downloaded from 3rd Party App Not Showing in Music App

Hello guys!

I downloaded the app called "Mxtapes" and I downloaded about 3 mixtapes, but I can't find them through the music app! I have to play the songs through the Mxtapes app, which doesn't have the prettiest UI. I'm also sure that it downloaded, because I turned off all my data, and all the songs played just fine. I'm running iOS 7.1 on a brand new iPhone 5c.

Thanks in Advance,
Intact Dev