AOSP is absolutely open source: the code can be viewed, modified, built and deployed as desired. There's good reason to be skeptical of Google-developed software, but your characterization of AOSP as "not open source" is simply not tenable.
Android versions in development are not open to contributions or community participation. Android is developed in secret behind closed doors. The end product AOSP spits out is open source, but to call it an open source project would be an extreme mischaracterization. And it is developed by Google, an ad company, not the community that eventually uses it.
Accepting external contributions is not a requirement of either Open Source or Free Software, and enforcing such a requirement is explicitly contra to the spirit of Free Software. The entire movement is about freedom, which includes the freedom not to accept downstream code.
