As far as i can tell it's not music, just a repeating sound effect, in which case compression van easily be that effective.
Yep, compression can do wonders. Let's say a piece of data is 1010110010110101 repeating 10^10^10^10^10^10^10^10^10^10^10 times in a row. (No I didn't screw up my notation there, that is just a massive number)
You cannot fit that piece of data on a hard drive uncompressed, yet I just communicated it to you in a compressed format and you can view the data accurately at any position.
Edit: That number in an easier to read format:
This could also be written as ¹⁰10
The music is stored in compressed form 7z, which as far as I can tell contains a few notes, a folder A that says "1000 x notes", a folder B that says "1000 x A", a folder C that says "1000 x B" etc in a long LONG string.
Except they made funnier folder names.
They didnt. Its a gimmick.