I have Messi as well and sent an e-mail to ESPN Soccernet. This was the reply from Dale Johnson:

As per the official How to Play game rules:

* The first was an own goal, which there are no assists for.
* The second came off the post, which there are no assists for.
* The third was flicked on by Burdisso.
* The final was an Aguero assist.

The How to Play states: A Key Contribution (assist) is awarded to a player who plays the final successful pass which leads to a goal. Please note that Key Contributions are not awarded to players who are fouled for free-kicks or penalties which lead to goals, for own goals or for goals which result from rebounds off other players or the woodwork.