That didn't stop companies making the phones and installing the OS (through a third party or with special permission, or most likely through a proxy). There was some fork in Chinese, which could be accessed.
Also, I think the App store was blocked, and a Chinese App store set up instead.
Also, python.org/downloads was also blocked (but not the rest of python.org). If you go to python.org now, there's a page labeled "Downloads" in Chinese for Chinese downloads which is not blocked. I guess it's easier to create a mirror than lobby to get a page removed from the banned list. It's weird though.
I think there was some Chinese version of android.com, but I don't know how close to the original it was.