In this case, this was already fixed by Apple's engineers. And like the article says, Citizen Lab (people who captured the exploit in the wild) and Apple have shared the exploit with Project Zero who analyzed it as well and wrote up that blog post.
Project Zero people have found numerous bugs in Apple's software in the past. They look at all kinds of software that's written by all vendors.
In this case, this was already fixed by Apple's engineers. And like the article says, Citizen Lab (people who captured the exploit in the wild) and Apple have shared the exploit with Project Zero who analyzed it as well and wrote up that blog post.
Project Zero people have found numerous bugs in Apple's software in the past. They look at all kinds of software that's written by all vendors.