Actually the 2.5K EUR fare is quite a standard fare in Europe, depending on dates/routing etc... BA offers these Ex EU fare as well. But for MXP-HKG return at this price, is pretty good.
Do note that CX does not publish its fares on ITA and other sources (similar to many Asian Airlines). that is why only local agents etc.. actually know about it.
Back to the question someone mentioned upgrade at airport, so I really doubt they will offer this fare when calculate the difference of the upgrade.