It appears YouTube uses some kind of software to match soundtrack content to copyrighted music. I've had them flag videos of mine. One time they were absolutely correct about the content, but the copyright owners graciously allowed it. I used a short clip of a 50s tune for the credits of a video promoting a folkloric artisan's work.
The other case was a lot like your experience, Matthew. Some outfit claimed the soundtrack to a video I posted with footage of a local junior surf contest. It was my video, meaning I shot it myself with my own camera, and I created all of the soundtrack music using Apple's Garage Band. I only used music loops that came with the software, which Apple expressly allows to be used for creating content even if it's for commercial use. In other words, it was 100% my song. Not that I really care about the stupid soundtrack, but I was offended by the wrongful and grabby claim.
I checked the song that I was supposedly infringing and it was some kind of techno music mix thing by some guy I've never heard of. Maybe he used some Apple loops in his song too? LOL!
I disputed the claim and the outfit dropped the claim. I guess they had to listen to my soundtrack personally to see if wasn't a match at all.
Should I register my crappy Garage Band soundtrack with the copyright office before someone STEALS IT?