OP - if you read the page you linked, the $10 option you purchased is detailed on the tab marked "Group 1 of General Boarding". It mentions the introductory $10 price. The only benefit listed is Group 1 boarding.

On the tab marked "Boarding and Flexibility Package" is listed the benefits in the e-mail AA sent you. Obviously, AA CS thought you had bought this package, apparently because you told them you had. The Boarding and Flexibility Package pricing varies by market and routing.

They are apologizing for your misunderstanding.