The phrase was first applied to software by the drafters of the Open Source Definition.

Be that as it may, it's a generic phrase, as evinced by its prior usage in other fields like intelligence and journalism. Lacking a trademark, OSI has zero authority to word-police everyone else. No amount of plugging their ears and chanting lalalala will change the fact that OSI does not own exclusive rights to the phrase "open source." Not with respect to software, not with respect to anything else.

The author of the project in this article is perfectly within their rights to use the term, and the rest of us know very well what they mean by it.