Like someone said in the comments, that might be in reference to country music.
I'm not sure I'd infer anything here. His friends apparently described him as a "conservative" from ROTC. He also voted a Republican ballot in the May presidential primary (that hasn't been reported in the media yet, but it's public record). More than anything, his Twitter feed seems pretty incoherent, so I wouldn't read into it much.
He also has a history of minor-league history of domestic violence arrests and weird behavior toward women. An ex-girlfriend apparently used to work at the Macy's where he opened fire, as well. It seems like there's a good chance there were no higher principles involved in this.
