It wasn't Bells fault anymore than Amini. The point of stunting one guy to the inside and the inside man outside is to cause just what happened. If they had been playing together Bell would have slid off his man and taken Amini's and vice versa. But they really haven't played that much together in the preseason given Bell is playing a new position and Amini missed most of last year. They will look at film and discuss what to do the next time. That is the point of preseason.
Bell was way more at fault than Aminu. Bell let his man blow right by him straight into the pocket. Then Bell is standing there with nobody to block and both he and Aminu are in perfect position to keep Aminu's man out of the pocket. Instead of blocking Aminu's man, Bell blocks Aminu out of the play. It would be like if Bell and Aminu were at LT and LG with just one d-lineman to block between the two of them, and Bell turned inside and blocked Aminu out of the play instead of blocking the d-lineman