Even though OSI clearly defines what "open source" means, it is sometimes (often even?) used as a synonym for "source available", as opposed to "free software" (which is the term that FSF promotes).
I'm not saying which term is better, just explaining why "open source" might not be objectively wrong in this case.
> Even though OSI clearly defines what "open source" means, it is sometimes (often even?) used as a synonym for "source available"
Where do they define this? In the OSI definition it doesn't mention having the source available for everyone, only that whoever has the program should be able to get the source[0]. I do believe it doesn't follow "open source" the development model where development is in the open and anyone can contribute.
I doubt there's anybody who uses the term "open source" that didn't just read it in the latest issue of CTO Monthly who'd argue against code under the AGPL being "clearly open source".
Being on Github doesn't make a project open source. Having a way for other people to easily contribute doesn't make a project open source. But being licensed under AGPL 100% does make a project open source.
I'm not saying which term is better, just explaining why "open source" might not be objectively wrong in this case.