It's like saying "freedom".

reading this:

https://en.wikipedia.org/wiki/The_Open_Source_Definition

"the definition is the most common standard for open-source software."

It is not exclusive.

saying "open source" does not describe a license. It is a generic term.

And the point is that unless someone points to a standard or a license, they can call their software open source, just show you the source with restrictions and use ambiguity to do different things than expected.