It is exactly the secret passage... Right now it's referenced only in the primrose loot table.
Judging by the fact that you aren't aware of that, it either weren't this way before, or you just decided on pulling it out directly from the database to share it with the world...
Most of us have this set by now. People do brag about their sets all the time.
By looking at the new look people will try to farm it specifically...
Thing is, it's an easter egg. Major thing here is the element of surprise.
Granted, there's nothing wrong with showing off a set you farmed. However there are people who doesn't play mp and won't immediately rush to farm something, especially when they're not aware of its existence.
A little wait would've been nice.
Edit: Good on you for at least hiding it in a spoiler.