I got a killer achievement for a killer I don't own

LadyFireHeart27

On steam

I got the "Complete the Evolution" achievement but I don't own the singularity and I was playing the mastermind.

I believe I got the achievement when I had injured or downed three of the survivors that were infected with uroboros.

It only just happened with the first game I played with the mastermind after I updated my game on June 21 2023.