Yeah, I was wondering about that, too. Granted, the BSD base is arguably one step removed from Apple (as that was NeXTSTEP, which Apple acquired), and both Darwin and OpenStep are open source. Apple continues to release the source of some of their software.[0] According to the "Myths" page at FreeBSD, "FreeBSD 9.1 and later include a C++ stack and compiler that were originally developed for OS X, with major parts of the work done by Apple employees",[1] so it hasn't completely been freeloading.

I don't know enough about the levels of contribution to either to make a strong comparison, and I'm more than willing to grant IBM and Red Hat make much larger contributions to Linux than Apple does to FreeBSD. And I sympathize with the desire to have more contributions. The "how Apple treated BSD" phrasing sounds like there is more active bad treatment rather than not contributing enough. Maybe the hiring of Jordan Hubbard is considered active bad treatment? (Honest question)

[0]: https://opensource.apple.com

[1]: https://wiki.freebsd.org/Myths#FreeBSD_is_Just_OS_X_Without_...