The guys on the radio side explained the ruling.So I found some further clarification on this. The reason they were able to advance is because Arenado threw the ball from the stands (which I can get him doing based on instinct). Had he thrown it to one of his teammates after he came out of the stands, the Arizona runners don't advance. He was interviewed postgame and said he was fine though he got treatment for about 30 minutes after the game.