These all sound like he's nervous being by himself and finds security with other horses. Pawing shows impatience usually, he probably doesn't like being tied.
He is tied short enough that he can't get into trouble, right? Like a hoof through his rope?
The owner just needs to work on more alone work. Maybe some re-focusing, sacking out, bonding, and reaffirming the idea that owner is herd leader and horse must respect and look to herd leader.
"Strength is the ability to use a muscle without tension"