Then who is an authority on the topic? Or are you trying to make a common usage argument, in which case you have to somehow demonstrate that's the way people understand it?

"Open Source" as a phrase does not. I have no idea what you mean by "Open Source as a concept," especially 1) because you're capitalizing it, and 2) because you're saying that the concept doesn't mean anything in particular.

It's annoying that people pretend like Open Source was a common phrase before it was invented to subvert Free Software by OSI, and it's shameful that people would tell this lie for the sole purpose of trading on the goodwill that Open Source software has created. Even in the world where people were always talking about "open source" before the OSI, that talk is certainly not the reason that people who are using the term to describe non-OSI approved licenses are using it today. They're intentionally trying to defraud people, and have the nerve to be snotty about it.