that armbar wasnt exactly perfectly executed. if you look back both of his legs were above tommy's chest. you have to have one leg over the face and another across the chest right below both arms. that was why tommy held in so long, because he wasnt being held down by ben's legs.
From what I can recall this is correct, in addition Ben didn't appear to be really tight against Tommy and he didn't get his hips elevated - otherwise Tommy's arm would probably be broken if he didn't tap. When an arm bar is done correctly, it is very easy to hurt someone seriously if you don't know your control.