That's right, the Venn diagram of Google users includes almost all Android users, a big chunk of Apple users, and even more too. In general I would assume there are at least 2x more Google users than Apple users, and even bigger disparity if you look worldwide.

In the US I believe Android/iOS is 50/50, but worldwide it's close to 80/20.

That, and Google's products are all data mines, so the Google stuff is probably much juicier.