I don’t think I see curling.
How long has the tank been set up?
How long have you had him?
Is the tank empty besides him being in there?
I’d think he’d feel more comfortable with places to hide. A lot of fish will just sit if a tank is lacking decor and hiding spots. I’d imagine it’s how we would feel in an echoy space in complete darkness. You’d be pretty scared to move too.
Another thing to keep in mind, most catfish are active at night. So I wouldn’t expect to see it move much when lights are on.
Visually it is a nice looking cat