Totally agree with you. If the basis of the arrest are as described by MacRumours, is ridiculous. Furthermore, it implies that companies should tap in real time all the time private conversations. Is my believe that telegram does strong E2E encryption and are deleted after a short after, much like a phone call, making next to impossible for a non participant to unlock it.
Such tap, should probably be possible but always done by judicial authorization specific to case being investigated. Not through mass surveillance, much less privately run with no supervision.