The connection on mine is not quite the same as I read your description, but what you said helped me to get it apart.
Here are two pictures that show mine -- just in case any others have the same problem.
First is a top view. In that view you can see what looks like a sleeve around the connection. That is actually part of the control side connection. To open, you have to press on the lever and hold the box side closer to the wires so as to not hold that sleeve.
Next is a side view which shows one long flat piece. It is connected to the control side of connection. Pressing on the end nearest the control pivots it up and allows it to pass over a small latch on the box side of the connection. That view is washed out because of flash, but it does show the lever hinge that needs to be pressed.