Sorry, that part of the article is meant to show that passing down promotion because u want to write code can be a mistake. Not that u will become a manager and still write code.

Like you said, if u love writing code try open source but higher positions still deal with some aspect of the software (planning, requirements, architect, etc) — code on higher/abstract level — which every developer should become familiar with.

I did not try to imply that as manager you will write code. Sorry about that