I'm not sure why these comments are so negative so far. If I'm understanding the article correctly, it is an optional setting to automatically open the app as soon as it is done installing. The Play Store isn't just installing and opening apps on its own.
Just like auto updates is a feature I turn off, and yet I still get automatic app updates (and I set all network use options to "ask", and it never does).
I've had the same problem across multiple phones since about 2015.