Got an answer. This is due to a checkbox being checked in course settings.

Launch SpeedGrader Filtered by Student Group

In this particular course, the box was checked.

This is a new feature, as mentioned in the September 21 release notes. 

I guess I should be paying more attention to the release notes. :smileyblush:

I have to assume one of the teachers or TA in this particular course checked the box because I spot-checked about 30 other courses and none had the box checked. Hoping it wasn't turned on by default for some reason.