Github is nice, but there is (and should be) far more to the open source world than just Github.
I am happy they are making sources available. It would be wonderful if Apple started developing their kernel in public (I would like to read those code reviews). What tools they use should be up to the developers.
I think he refers to the fact that we don't get the real version history, with informative commits which may provide context for the code in question, but instead just get snapshots for particular versions.
I'm not saying it's useless, but it's certainly much less useful than a proper version-history, and very much a declaration that it is in no way intended to be a collaborative project.
But I guess that shouldn't surprise anyone either. It's Apple, after all.
Apple's made some pretty big genuine contributions to open-source: WebKit, LLVM[1]/clang, Swift, OpenCL.[2]
[1] Yes, technically "not Apple" in the sense that Node.js isn't Joyent.
[2] Admittedly partial credit at best since they've orphaned it in favor of their proprietary Metal API. I'd guess however that Metal will get open-sourced pretty soon.
For a long time, they just did source-code dumps whenever they made a binary release (i.e., did what is required by the LGPL). They actively chose to move it to being run as an open-source project, with public history, public bug tracking, and public contributions.
I am happy they are making sources available. It would be wonderful if Apple started developing their kernel in public (I would like to read those code reviews). What tools they use should be up to the developers.