Atziri's Reign dropped from enemy instead of from corrupting a jewel

https://imgur.com/a/vxTfJbd

Atziri's Reign dropped from a monster while I was clearing out the Twilight Strand in the beginning of act 6.
I am honestly not sure if this is a bug or not, but I couldn't find any information about the item dropping from a monster only as a outcome of corrupting a crimson jewel.
I am also unsure what monster I killed that dropped it, but I was within the part of the zone that would be copied by the mirage, but I was not within the mirage itself.

Bug report reference ID: 3,034,487,765