The self-destruct was triggered due to loss of control.
“14 seconds later: The range safety officer sends a self-destruct command. The rocket explodes into a fireball over Wallops Island, Virginia.”
http://abcnews.go.com/Technology/moments-leading-antares-rocket-explosion/story?id=26539879
It’s great to see the self-destruct being triggered after it hit the ground.