Unfortunately, we have a similar problem. For us, I think it's more that everyone is excited and cheering, etc....so Bentley gets really excited and runs around barking.
The same is true when we're watching football (a lot!), and someone scores. We cheer, and Bentley barks and barks!
It's hard for him to curb his herding instinct when our energy is up and we're jumping and yelling.