A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
Stock Images is a new feature; the images are licensed by Microsoft from (as you've found) Getty, and possibly other sources, to be offered to PPT users in their presentations.
Most of us here are not MS employees and none of us is an MS attorney, but some of us have asked these same questions of the people at MS who developed this feature.
The general advice is that you can use the stock images in your presentations and use the presentations in pretty much any way you like, including ways that produce revenue. You cannot, however, sell the images AS images.
As you already understand, the creative commons images are another matter; for those you'd have to check the licensing individually.