In general yes.

China can block ports entirely. But nostr is run on port 443 generally and they don't broadly block web traffic. So they have to block relays specifically usually by IP address and domain name. Unless they have found and blocked all the relays, they haven't blocked nostr. I've received a message from a person inside of China within the last 3 days (on popular relays even) so I don't think the've blocked relays at this point. I expect they will block relays at some point in the future en masse after they believe they have found enough of them for the blocking to be effective (if they just block them as they encounter them, people will migrate and it will fail for the same reason that vaccinating into a pandemic fails).