Like most things open source is a continuum of subtle differences rather than a category.

In my opinion the following software is much more open than Android:

Linux, Apache, FreeBSD, OpenBSD, GCC, clang, and generally most open source products developed by the community.

In my opinion the following software is less open than Android: C#, OSX, iOS, and generally most software developed by major corporations.

The real keys are that your Android device is locked down, fixing it voids your warranty, and development does not take place in the open, rather every few months a major patch is released and there is no way for the community to contribute to the project in any meaningful way.