My custom textured metahuman has a good eyelid texture though I haven't made it. How could this happen?

Hi, I made a custom base color texture for metahuman,
and it looks really great, but quite confused how it works.

Could you see the attached? My base texture has an artifact around the eyelid,
but somehow, this is not included in the rendering result, and the eyelid looks beautiful.
How does this work? I’m really curious about this.