Using the "is joining" phrasing is a classic way to try to spin an acquisition as some kind of partnership. 99% of the time, it's definitely not.

I literally thought that, clicked hide, then thought "Wait a minute, do they mean...?" and had to go fish it out of hidden items.

"Joining" is an interesting term here... but I suppose it won because it sounds more like something friendly humans would do. "NPM Is Breaking Bread and Sharing with Github as Special Friends."