They're literally doing the opposite, right now you can't install a custom operating system, but in the near future you won't be able to install custom apps either: https://keepandroidopen.org/

What do you mean you can't install a custom operating system? The bootloader is unlocked on google phones, isn't it?

You can install a custom operating system on (a non-carrier-locked model of) every phone Google has ever made.

This website is full of false FUD.