Surely it does, if there's no way to point back to the specific user. The best one could say is "someone using this username posted this message at this time, but we can't tell who that was".

I accept that if someone data-mined every comment by said user, they might be able to build a picture of said user clear enough to identify them (e.g. posting times might indicate likey country of origin). Possibly, depending on the content they posted.

(I'm just thinking around the problem. I'm not a security/privacy researcher designing systems I'd like others to use, just an interested user curious where the lines in the law lie, and also what the threat models might be to me as a user.)