As somebody who's used blender for years and experimented with the denoisers, I thought so too. The inputs you usually give denoisers are the rendered image, the albedo of every pixel, and the normals. Denoisers can struggle with reflective surfaces because the albedo and normals match that of the surface, not what's being reflected in it, and so offer no real help to the network- which would explain why this single spot is where it showed up. I only commented because I found it funny. It's such a tiny detail, it doesn't detract from the art at all, and I only noticed it because I'm used to hunting for stuff like that in my own renders. Having everything turn out perfect except for one stupid thing you didn't notice until after you posted it is extremely relatable to me