The armbar is the finish, but the setup is that she REALLY good at getting in side control. Plus Carmouche is still raw like sushi, while ROusey was raised by a world class judoka.
You can't beat Rousey if you can't keep her from getting both legs on one side of your body. Sooner or later, she'll isolate her whole body against your arm. There are guys with enough upper body strength to keep a 135 lb woman from getting the armbar from that position. but another 135 lb female? She might exist, but I've never seen her.