In the early history of Wikipedia, a "newbie" was defined as a user among the newest 1 % of all users (mainly because at that time the registration date wasn't stored with the account). This has changed a long time ago, nowadays the definition of the contrary "autoconfirmed" usually includes all users registered some (eg. 4) days ago (and sometimes some edit count etc.).

Special:Contributions is the last place that still uses the old definition. I think that for consistency this should be switched to be based on the autoconfirmed user group, too.