What this API does is very limited. An API allows programmers access to some part of a system that you’re unable to use without. So it might be all of Reddit’s data, or could be as limited as allowing a webpage to access the back en forward button of your browser. Both are API’s.
The history API allows a webpage to navigate to the next or previous page where you were, without knowing what they are. It’s the same as pressing the “previous“ button by hand. Disabling it will probably break navigation within some sites (besides; don’t think it’s possible or sensible to disable).
This seems harsh. Maybe they should just lose their patents sooner.