This person had a visual perception disorder called prosopometamorphopsia, which causes them to see distorted faces on humans.
In his case, the distortion didn't occur when seeing them on screens or on paper. So researchers were able to match what he was seeing in real life to what he was seeing on screen. The left side of each image is what the person actually looked like and the right side is what he was seeing.
The disorder doesn't cause delusions. The people can recognize faces, but they just appear distorted.