Just saw this:
a 1400 rep new user? Wow! He's learning fast until I clicked his profile and he's a 2 YO user?
This is by design. First, the meta site and the main site are considered separately in this regard: the activity on one does not affect New Contributor status on the other. (Reference). You are seeing the icon on meta.
Second, the criterion is the age of the oldest non-deleted post on the site, not the age of account. From the spec:
To set the bit, we look for a user's oldest non-deleted question or answer. If one doesn't exist or that found post is less than a week old, we mark the post as OwnerIsNewPoster.