The background read says it well, Android IS open source, only the Google apps sources aren't, so my point remains valid.
Um, have you ever tried to use an Android device that doesn't have the google stuff? No maps, no play store, no gmail, no google services at all? Amazon are the only ones who have had any success with such a fork, and they do it by being closed source.
The core of "Android" is open source. However, the vast majority of devices running Android are not open source. You can't take the device, recompile from source, and do what you want with it. Locked boot loaders. Locked modems. Proprietary skins. Bloatware.
Back on topic of Tesla open sourcing it's patents - the terminology is wrong there as well. They haven't open sourced anything they don't seem to have even open licensed anything. Just said that they won't sue if someone uses their patents 'in good faith' (whatever that means).