Telegram suspects that Apple is trying to appease Russian censors while keeping a low profile and plausible deniability. Perhaps Apple is buying time and showing goodwill to Russia while they negotiate a deal - who knows?
Acting on their suspicion, Telegram makes this announcement, putting pressure on Apple to unblock updates, or at least to stop stonewalling them.
It's a clever use of PR as a tactical weapon. And assuming that Apple was indeed stonewalling Telegram (extremely likely knowing Apple), I think it's perfectly justified.