called for obstruction, but you can't have two players "in the act of the fielding the ball" at the same time. One of them was fielding the ball (turned out to be Otero) and the other (Moss) was obstructing the base path causing the runner to alter his route to the base (contact is not required, just altering his path).

As for why Aybar ran to the inside rather than the outside, both fielders' momentum was taking them into foul territory until they collided with each other stopping them in their tracks. His best option to avoid a collision was coming inside away from where he thought the play would end up taking them. I don't think he intentionally caused a collision to try for the call.