You'll find that some geckos just really take to hiding under paper towel.
I'd say half of my geckos like to hide under paper towels during the day, though I often find them in different hiding spots. Nighttime activity isn't exactly "100% active when it's dark", so you just probably haven't caught it being out and about. From what I saw when I used to spend hours watching their behavior, most of my geckos don't turn on at 'first dark', but wait until I've had the lights out for an hour or two before they get around to mating/eating.