Indept is correct.
Not to be a jerk, but the "ECO light means MDS is active" is a common misconception, repeated over multiple forums. I believe that that may be what Chrysler intended in Hemi vehicles that have MDS, as the "ECO" mode light, or "fuel saver display" as I believe it is called in the manual, and the MDS system supposedly have similar parameters that they look for from the computer. Other than calling MDS "fuel saver technology" and the ECO light "fuel saver display", the manual never states one is actually a signal for the other. Maybe its what FCA wants you to assume, but they never actually come out and state it.
And even they did state it directly, it wouldn't matter. They are not directly connected.
If you read enough posts on forums, you'll find some guys that have gone so far as to rig up a light to the MDS system, and the ECO light will be on sometimes when MDS is not. And some tuners can shut off MDS completely, but the ECO light will still function.
As a disclaimer, we do not point out your mistake, slacadjuster, to try to ridicule you or anyone else. We are just trying to educate. Hope you don't take it the wrong way.