I don’t know what they actually do but one possibly is to look for (absence of) the TLS handshake. Or maybe they simply infect all devices on the Chinese market with MITM certificates to be able to decrypt all TLS encrypted traffic. Should be easy to force companies to do that in such a country.
The port isn’t their focus, they’re looking at the protocol that is being used, regardless of the port. The protocol is still visible when not doing deep packet inspection. That’s why there suggesting a socks proxy for Russian citizens, because that uses HTTPS to tunnel traffic, so it wouldn’t be caught up in protocol analysis.
can you maybe link some ressources on how the protocol used can be detected? i did not know about this and would like to read into it some more :)
Look up NBAR for the basic idea. Each vendor has their own ‘secret sauce’ implementation, Palo Alto only needs 9 bytes of payload for disambiguation, iirc.
