There seems to be some confusion on the part of Boubouille on how and why certain items are popping up on PTR before bosses are killed. From my understanding of how loot works in instances, the loot is seeded on everything in the instance as soon as the first person zones in. I believe this means that since the loot is "on" the boss, you merely need to target him to "unlock" whatever 2-3 drops he has and be able to see and link them, assuming you know the item ID. This is why Brutallus loot was appearing before anyone killed Brutallus and why Felmyst loot was appearing before anyone killed Felmyst.

So just because a new piece of loot appears, does not mean that anyone has downed a new boss. I could be wrong about this of course but it seems to be whats going on.