I guess you're right, in the way that we can either describe and prescribe language, and yes, open source is not defined in exact terms. I still do think that attaching the label to a product, and disregarding the decades long collaborative nature of the development is utter nonsense. In my opinion, the onus is on these people to get closer to what open source really is, not because I don't want to update the term, but because I want the movement to succeed, and not to be watered down.
Funnily enough, the Liquibase project agrees with this sentiment too (or wants to avoid the fallout from open source gatekeepers): https://github.com/liquibase/liquibase/pull/7380