It makes no sense to you. But there was shooting at more than this concert. The confusion created my a mass murder is more than enough chaos for a hit squad to use for their escape. the ‘hamdlers’ on scene at the Boston bombing melted into the masses.
I don’t doubt it. But it’s too weird to plan it out. “Hey, there will be a concert that day. And if anything goes wrong with our plans, Boss, Jason Aldean will be on his last 4 minute song right at that moment, so we can shoot upnthe festival goers and get away just in time.”