Martin's article pleads with readers not to be pedantic when using the term, but offers no alternative definition, beyond 'let people use it when they can read source code'. Perhaps that's the proposed usage you and Martin prefer?
If I'm understanding your position correctly, perhaps you would agree that Ocarina of Time has now been released as open source?
https://arstechnica.com/gaming/2021/11/reverse-engineering-t...
If so, the term is uselessly vague, as it says nothing about the rights of the licensee. In this sense, 'Free Software' has much more meaning...perhaps RMS was onto something!
If the OSI picked a term that wasn't simply descriptive they could trademark it, then they could enforce their definition and there would be no ambiguity. That would be better for everyone.
“Open source” has older non-software uses, most notably in the intelligence context, where it picks up sharply in the 1980s:
https://books.google.com/ngrams/graph?content=open+source+in...
You can see the term gaining popularity prior to 3 Feb 1998, and there are references to for example BSD being 'open source' as far back as 1990.
https://books.google.com/ngrams/graph?content=open+source%2C...
Via https://www.arp242.net/open-source.html.