If the tip is certifiably genuine, then that's very odd. Could it have come with some protective coating rather than excess oxidation? Although i've never seen that with Metcal.
That said, I've personally never been a huge fan of Metcal. The stations are expensive, the tips are expensive, they do work quite well arguably, but I tend to prefer being able to adjust (and monitor) the temperature.
One area where these shine is production, where always using exactly the same temperature is just a matter of providing the right tips to operators and doesn't rely on them setting temps correctly (and I've seen many cases, over years, of operators setting temperatures consistently way over the ones specified in procedures, usually with the rationale, when you asked them, that they believed it made soldering easier.) Just my 2 cents.