There's a term for "proprietary projects whose source is available on GitHub", namely "source available". "Open Source" != "source available", and attempts to describe one as the other are clearly attempts to deceive
As I recall "Source Available" is a lot worse than what Sentry is proposing. It usually required signing an NDA or jumping through some other hoop in order to get the source. This is much better than that so I don't think it would be properly descriptive.