They were referring to some apps ignoring your default browser preference and opening Microsoft Edge whenever you click any link in the app. That's not a niche case, it's an everyday interaction.
Literally nothing stops any app from hard coding launching msedge.exe or chrome.exe
But why ignore the user preference?
So Bing has non-zero MAU due to people accidentally clicking links on the Windows lockscreen to "learn more about this picture"
This is about integrated Windows functions from Microsoft that force the use of Edge. That constitutes anticompetitive behavior by Microsoft, besides ignoring configured user preferences.
The law does now. There’s a default setting for a reason.
Are you sure they were ignoring defaults and not just using edge deeplinks. It's not much different than apps like slack who always use a packaged in chromium instead of your default browser's web engine.