I think you might have misread the article (or maybe I have?). I think the article is saying that other people (a 3rd party that is not Meta) can use some metadata clues to puzzle out which OS a user is using WhatsApp from. The article then says this is bad because an attack can target specific OSes or tailor their attack to the user’s OS. Eg. Hacker has an evil link that abuses an exploit on Android only. They can figure out who is signed into WhatsApp on android and only send those people the evil link.
Shocked I tell you. They were fingerprinting all along.
I think you might have misread the article (or maybe I have?). I think the article is saying that other people (a 3rd party that is not Meta) can use some metadata clues to puzzle out which OS a user is using WhatsApp from. The article then says this is bad because an attack can target specific OSes or tailor their attack to the user’s OS. Eg. Hacker has an evil link that abuses an exploit on Android only. They can figure out who is signed into WhatsApp on android and only send those people the evil link.