It was a reference to a Southpark episode in which the kids try to smuggle a goat onto a military cargo plane to send it to a poor family in Afganistan. In the episode, Stevie Nicks was to perform a USO show for the troops at the same base. As they walked past a checkpoint, the goat bleated and the MP said something like “Hello, Ms. Nicks”. It was making fun of how similar her voice sounds to a goat.
Gotcha. Post that clip if you can find it. We’d all get a chuckle.