Received Eldritch Voidstone without finishing Searing Exarch progression

I currently have the Eldritch Voidstone socketed in my Atlas without ever having encountered or killed Searing Exarch.

Reproduction steps should be as follows:

1. Complete entire Eater of Worlds quest chain, including quest invitation.
2. Advance Searing Exarch quest chain to Tier 14 (Pursue the Searing Exarch's influence in a T14+ map).
3. Have a party member kill the Eater of Worlds in their map device off a regular (non-quest) invitation.
4. Enter the encounter after the Eater is dead.
5. The Eldritch Voidstone should be on the ground with the Eater's loot.