Author of article here. Thanks for kinds comments.

Yes, it's possible to stabilize bottle rockets with fins (to adjust the CP), but as the article hints, the stick is multipurpose in helping with launch, as well as stability (plus being easy to manufacture with low precision).

I just published a follow-up article talking about bigger rockets. http://datagenetics.com/blog/july22020/index.html

Aeronautics is a complex science and my articles are intended to pique interest, not oversimplify or belittle. It's a hard balance to explain things in a few hundred words. I hope you enjoy them and, if there is interest, they become the catalyst for you to learn more. It's a fascininating subject.