One might suppose that because login relies on the cellular network it's implicitly part of the app's infrastructure. In that sense the technical failing of Telegram was relying on one method of authentication (when multi-factor should be the default). I think it far-fetched to extrapolate that into 'Telegram got hacked', though.
I understand the want to share the article, but a concerted effort to amend the original title to reflect the actual content would have been appropriate here, methinks.
Edit: fixed some speling.