Quick question... Is ULTRAKILL considered an indie game?

I'm asking this because I've seen many people rating/reviewing/recommending other indie games like stardew valley or the binding of Isaac but very rarely ULTRAKILL.

Is it because it's not as famous? Or am I just stupid for thinking that?

Also image unrelated

I'm asking this because I've seen many people rating/reviewing/recommending other indie games like stardew valley or the binding of Isaac but very rarely ULTRAKILL.

Is it because it's not as famous? Or am I just stupid for thinking that?

Also image unrelated