I am inclined to agree with you. The "art" sounds about as convincing as a demonstration of the value of the UV, as it is convincing as a demonstration of the value of the art, but it certainly suggests that there is nothing magic about the UV lights as fly attractants.

The fact is that to insects UV is just a coloured light. If the species is one that is attracted to light, then it will like the UV and go there. This is a common basis for light traps as used by entomologists at night in a dark situation! During the day, or even on a bright, moonlit night, you expect a reduced catch. Even at night you expect more moths and beetles than flies, and you seldom find many flies anyway, especially day-flying flies like houseflies and bluebottles.

I speak from experience; I managed a light trap for a few months as a student.