Zone 2 is Silver Medallion and elites on Delta partners. Prior to becoming SM, I did have an exit row one time and was given zone 2. Zone 1 is GM, PM, and DM. And, of course, now there is Prem for First Class. Enjoy!^

Edited to add: I just looked at your profile and noted that you are an AmEx Reserve holder. That may have something to do with the Zone 2 as well. Seems like I remember reading that gave you priority boarding.