So after looking at page one again and seeing your pics I see you do have the WB sensor from the AEM kit and havn't installed it yet.
I think I was spot on in my last post and what you have going on is that the narrow band in the stock location in the rear manifold didn't get capped...they just left it there and unplugged it. The turbo kit changes the location of the stock narrow band and moves it to the downpipe and they just installed a new narrow band there without capping the rear manifold which is no big deal really seeing it's sealed.
You'll want to have a new bung welded in and installed a little futher down the downpipe andread your aem instuctions for best location for the wide band o2 sensor, maybe have the old narrow band thats in the rear manifold pulled and cap the bung hole while your at it.