Stevie does look as if he is escaping as the ref stops it, but remember the ref is only human and has the fighters best interests at heart.
If the armbar had stayed on while Stevie rolled/turned to escape it could have twisted it as well as hyper-extended it at the same time and i think this is what the ref thought was going to happen so stopped the fight before any serious/lasting damage was done.
Would like to hear Amro's take on the stoppage but i think it will be similar to what i said as that is what i would have thought if i never knew the outcome before seeing the fight.
A rematch is merited i think on Stevie's part, but i would still stick by my initial prediction Dan to take the win.
And remember the ref can't watch it over and over and then make his decision.