Yes, it uses hidden services; I won't know x23ff...sds is you. However, the most plausible link between me and evgen is HN, so x23ff...sds appears on both of our contact lists, it's likely to be a HN user. More widespread analysis of contact lists can probably tell us who you are. (So you know evgen and me, but not RickRoll? That gives me a good idea of who you are...)

This is one reason why it'd be good to use different IDs for chatting with different people. Unfortunately, Tor wasn't designed to work that way, so you may need to run multiple clients or something similarly annoying to get this to work.