From the article:

> Later, several Telegram users said they could no longer use the messaging app after local carriers complied with the ruling. Google and Apple were also ordered to block the app.

So yes, apparently they can. Or did you think it needed Telegram's cooperation?

Even if it is possible to install apps manually, most users are not "power users" able or even just willing (or willing to learn) to do that. Another aspect of the much more curated software world of Android or iPhone vs. PCs, where blocking would indeed be mostly useless even for regular users.