No it means you can't use wrist detection to auto-lock because the metallic pigments in some tattoos interferes with passive skin sensing. There's an option to turn it off.
How many people have metallic pigment tattoos on their wrists?
How many people have metallic pigment tattoos on their wrists?
The watch works fine.
AFAIK, very few, because optical pulse oximeters usually go on fingertips or earlobes, even ones that are attached to wrist-mounted displays.
Edit: on people with dark tattoos.