Can't back their claim, but..
> How do you explain that Android smartphones has grown even more than iOS, despite the fact that they allow you to install whatever apps you choose?
1. Android is free for OEMs, iOS is unavailable. If you want to make a phone then its a great choice, and a free one.
2. Most flavors have a dominant store built in (android store, amazon store, Chinese-oem stores like Xiaomi) that are "safe" or offer that illusion. The important thing here is the built-in-trust of the default settings
3. Piggy-backing off point 1, cheap phone OS means people can make cheap phones -> Cheaper leads to more available for more people, and most of the world is poor compared to US iPhone users