Honestly, being a public forum it is right that, unless you keep the profile private, anyone can see your generic statistics (reading times, how many posts you have published or how many likes you have given / received, etc.) but a normal user shouldn’t know who invited me. I mean, I don’t understand why a “correlation” should be public. There is a reason that when you sign up for online games, only you and whoever you invited know about this. If I go to a user’s profile, I can’t know if he has been invited by someone or not. It is something that exists only here. And you can’t say it’s not a privacy issue. Here we are dealing with “user correlations”, not just public activity information in the forum.
For the solution given above: hiding with the CSS does not imply that the information remains publicly visible. And what I’m saying is that it just shouldn’t be that way by default.