It's not clear who made Telegram's crypto but it was probably Nikolai Durov who is a genius mathematician and engineer, so it's not like it's some guy in a garage.
So, yes. He (or any of the other 6 world champion coders that were bragged about) designed a broken protocol. Broken, as in "trivial access to the plain text by the server", which is pretty damn awful.
When people say that telegram rolled their own crypto that mean that they chose weird crypto primitives, weird key handling and generation and combined them in a way that made people go "whoa! That looks weird" and defended it by refering to their own world championship victories, by extension saying that people were to stupid to understand.
And 6 months later their protocol was shown to be broken.
Use telegram all you like. Don't say that their encryption is even close to being the gold standard.
Telegram's on the other hand, can't be continually audited, but the MTProto scheme they put together has been found to have a number of flaws [1], and that hasn't changed. They also haven't really allowed third-party audit of their actual code, so there may or may not be extra bugs waiting to bite you.
Kids these days, can't keep up with fashion