On most other IRCds, +p marks a channel as private which hides it from /whois and /list replies, while +s marks a channel as secret which stops /names and /who queries from users not in the channel.
Ora doesn't have +p (which is fine, it's a bit of a weird half-way house), but its +s seems to act like +p on other servers -- i.e., an unprivileged client can do a NAMES or WHO request against a channel with mode +s and receive a full list of users in the channel on Ora.
The Ora manual documents this behaviour but it's kind of confusing for anyone used to the normal semantics, and I can't see a way to actually suppress NAMES/WHO queries for channels.