I do not know what technique this app used, but in practice apps are more resilient. It has been shown by Telegram which more or less successfully evaded blocki

I do not know what technique this app used, but in practice apps are more resilient. It has been shown by Telegram which more or less successfully evaded blocking in Russia. I think it's a combination of lower-level network API, traffic obfuscation libraries, push notifications, and hosting some info on public services which cannot be blocked without affecting too many people. But it is just a guess.