It's not the site's issue, it's Stallman. Even if they didn't intend for it to be a strict Open Source site, it has Open Source in the name which Stallman wouldn't participate in. The same way Stallman won't participate in (at least at the time of writing this comment) shows or conferences that only use Linux in the name and not GNU/Linux. For example he won't go to something like Ohio LinuxFest and the Linux Action Show had to rename itself the GNU/Linux Action Show to get him to come on. For some people the work of changing the name is worth it, for others it's not worth the hassle.

OSDEM conference even renamed itself on request of Stallman https://en.wikipedia.org/wiki/FOSDEM#cite_ref-3

> Yet much of this software is “open source” — a technology commons that can be freely used and contributed to by anyone, but at the same time, is controlled by no one person or corporation.

That's pretty much the definition of free software; so yeah... Weird choices.

No it isn't. Free software is about specific software freedoms originally defined by the FSF which overlap, but are not quite accurately captured by that statement. So yeah, Stallman would object because he's all about such fine distinctions.

If I recall correctly there is only one or two licenses among hundreds that aren't both recognized by the FSF and the OSI. The differences are largely ideological, not technical/legal. I'm a fan of Open Source but my main side project is under GPL v2.