The fact that Signal was blocked but WhatsApp remains usable has prompted speculation by Iranian users on social media that Iran’s government somehow has access to users’ information on WhatsApp.

Well Duh! Of course, and rightly so I would think. These platforms are pretty much all US based and while the NSA no doubt has access to them the Irainian spooks don't. Why would they tolerate secret encryped U.S. based traffic anyway. They no doubt don't want their population to end up like the U.S. population and we can't blame them for that!