Since this is touching Linux, and Linux is copy left, they _have_ to do this.
In addition to the other comments about the fact that this wasn't forced to adopt the GPL, even if it were, there's nothing in the license that forces you to work with the community to take contributions from the public. You can have an entirely closed development process, take no feedback, accept no patches, and release no source code until specifically asked to do so.
They don't have to do literally any of this.
Touching Linux would not be enough. It would have to be a derivative work, which this is (probably?) not.
Besides, I think OP wasn't talking about licenses; Apple has a lot of software under FOSS licenses. But usually, with their open-source projects, they reject most incoming contributions and don't really foster a community for them.
> derivative work
Or distributing builds of something that statically links to it. (Which some would argue creates a derivative work.)
If the license of this project were determined by obligations to the Linux kernel, it would be GPLv2, not Apache License 2.0!
The comment was about them welcoming contributions, not making it open source.