The most interesting part of this ThreatPost report is where they share some background on Sadegh Ahmadzadegan and Omid Ghaffarinia, the researchers who claim to have uncovered the flaw in Telegram:
Regarding claims by the Iranian researchers, Telegram's Markus Ra told Threatpost that the allegations were "click bait fear mongering" on the part of the researchers.
Both Ahmadzadegan and Ghaffarinia, who co-authored the research on the Telegram flaw, self-identify themselves as two of seven accused Iranian hackers indicted by the U.S. Justice Department in March for state-sponsored hacking of U.S. networks and targeting U.S. industries.
According to the indictment, Ahmadzadegan and Ghaffarinia are accused of working for the Iranian Revolutionary Guard Corps and carried out DDoS attacks against 46 U.S. financial institutions.
You can find the US Department of Justice indictment against Ahmadsadegan (also known as "Nitr0jen26") and Ghaffarinia ("PLuS") here.