Music Publishing Rights Collecting Society

Someone YouTube calls "Music Publishing Rights Collecting Society" has claimed copyright ownership of the music in my (512) Brewing Company Second Anniversary video. In theory, this work is in the public domain. I got it from Musopen, a repository of recordings of compositions in the public domain (both the compositions and recordings are in the public domain, since there is separate copyright for the performance and actual sheet music).

According to Musopen, the music I'm using is Holst's march from Suite No. 1 in E-flat. Holst has been dead for something like 75 years, and the work was published in 1909, which would put the composition is in the public domain. The recording I'm using was supposedly recorded by the United States Marine Band, so it shouldn't be copyright protected.

So, am I accidentally using a copyrighted recording (and Musopen made a mistake about the origins of the music)? Or am I dealing with a copyright troll?