I'm not sure what point you're trying to make here. You start by agreeing that telegram is simply not private. Then you move on to implying that it must be, because the CEO got arrested?
How does that change the fact that it is, by your own assessment, not private?
To answer your question, the answer from my perspective is quite simple. Noncompliance. If telegram had complied to local laws, like the others have and continue to do, he would not have gotten in trouble.
Not much of this makes sense. Maybe we don't have an equal understanding of private. If thats the case, this discussion is going nowhere.
I will point out, though, that this is particularly nonsensical
Telegram doesn't use encryption. Everything is in clear text. Nobody needs a back door to get access. Not even governments. It's all just out in the open