Telegram desktop [1] aka "tdesktop" is the official telegram desktop client, it's based on Qt and it's cross platform (Windows, GNU/Linux, OS X). What you have been using must be "Telegram for OS X" [2], a different application entirely, which supports only OS X obviously. IIRC tdesktop didn't support OS X initially.
[1]: https://github.com/telegramdesktop/tdesktop [2]: https://github.com/overtake/telegram