Read his question again. He didn't ask how to do it, he knows that. He asks why it works.

I was wondering the same thing when I read the article - my best bet is that the idea of ‘cracked’ G-Suite keys is a journalistic fiction invented for the sake of the story.

Not that it's legal for them to distribute it when they are not certified, but I don't think that there is actually a key required.

You can open the .zip and replace the keys or clockworkmod which cyanogenmod uses allows it to copy from recovery by ignoring the fact keys are different from platform. I guess since they just provide binaries and not source, and google makes money when you use their apps and provide them data they don't care that other projects have GAPPs for dl