Words have meaning and sometimes it's important to remain clear. I think it is not acceptable to use "open source" for things that are not actually "open source", especially in an article about the topic. There are probably better words to describe what needs to be described instead.

See my other comment [1] where I try to defend why I think like this.

(Now, as I'm saying in the other comment, in this case for this article, it's just an example that doesn't work, it's not something fundamentally wrong about it.)

[1] https://news.ycombinator.com/item?id=43613453#43614394