Get news to see other services following in the footsteps of WhatsApp!
You shouldn't throw around accusations without proof.
The word "broken" means susceptible to practical attack, and attacks aren't always of the "cryptanalyze the ciphertext and read the plaintext because you're a clever mathematician" variety.
For example: Padding Oracle Attacks. This is the most accessible explanation on-hand: https://twitter.com/SoatokDhole/status/720435675401744385
A padding oracle attack lets you decrypt a message by studying how the cryptosystem responds to garbage input. Without recovering the key.
iMessage had a compression oracle attack recently: http://blog.cryptographyengineering.com/2016/03/attack-of-we...
They didn't merely "read the plain text of the traffic [they] capture[d]". But these systems were still, quite badly, broken.
So what's my point? Telegram's protocol is susceptible to the same class of active attack. Thus, it is broken.
iMessage would have been reasonably secure had they used AEC-GCM or a MAC. The design at least made sense: compose a scheme out of known primitives. They just missed (very important) details. Telegram is just turtles all the way down.
I'm not trying to imply that WhatsApp are the first secure chat, but I am saying it is the first major platform to switch to end-to-end security and this looks like the first step in a trend of switching.