Article fails to answer the "why"

I found this story interesting, but I have questions.

Members of a close-harmony group from Yale University are recovering after being ambushed and beaten up while on tour in California.

Members of the a cappella Baker's Dozen were performing at a party in San Francisco at the new year when their rendition of the "Star Spangled Banner" apparently sparked taunts and threats from fellow partygoers.

As the group left the house, they were attacked by dozens of assailants, suffering scrapes, black eyes and concussions, said Connecticut's News Channel 8.

The article didn't say much more than that. Here are the three questions I had:

1. Did they get beat up because the San Francisco mob hate America and were upset by the Star Spangled Banner?

2. Did they get beat up because they sang an offensive "rendition" of the Star Spangled Banner and offended the fellow partygoers?

3. Or did they just get beat up because they are in an a capella group?

Update
It looks like it may have been number three.