There wasn’t any legal ban. RosCommNadzor slowed down TG like they recently did with YT (it can barely load a music track without VPN) without any court decision because they can, it went for a week or so, and then it was lifted. Nobody knows why, but there is a suspicion that TG started to cooperate with russian authorities, in a non-automatical manual manner. Some suspect it was a PR campaign to make it as popular as it is now.

It didn’t leak stuff as far as I know, that’s done by bots like Глаз Бога that accunulate all info on a person and frequently used in OSINT and deanon\bullying, but blocking popular bots and channels that are too annoying to Russia is what they do. From the top of my head: CleverVoting (Умное Голосование, УГ) channels from Navalny’s team*, channels for cooperation of protest of soldiers’ wives, separatist channels from Bashkortostan and other places. I’ve seen iranians also posted that they had their protest channels banned - and Iran and Russia banned free and popular VPNs at the same time, spoiling their cooperation.

* Durov’s public comment on that gave birth to a meme. He implied that there are just two ways: either banning it from TG or having TG banned on the whole territory of Russian Federation. As a copypasta it was transformed millions of times, and if it hasn’t lost it relevance, we could’ve probably seen a boykisser version of it.