It's not part of the content area, but above it. The browser decides what it paints in its window. And apparently Microsoft thinks pushing an ad above a competitors page is a good idea.

To the people who care, it's another reminder on why they don't trust Microsoft. For the rest, it's just another ad. Disregarded.

Edit: I find the term "inject" in the article's title to be misleading, because it sounds like doing HTML injection. It's more shoving than injecting.

I would bet they have a "hidden" extension embedded in edge, that just injects a content-script

It's in Edge, they control the browser and everything the browser does.