It's pretty common on boats without a liner or nothing on the inside, Most likely the gel coat or paint is thin on the boat.
I wouldn't say it was anything to be concerned with.
The gel coat on my old portager 22 had a few scratches and scuffs, but was in overall decent shape when I got it, but after pulling the carpet out of the interior it 'glowed' inside, so I decided to go ahead and paint it.
if the exterior is nice, you can paint the interior if it bothers you.
EDIT: Many boat builders used the translucent characteristics of fiberglass to provide light, cape cod marlin for one a few pics shown in the thread here:
The Plastic Classic Forum :: View topic - Cape Cod Marlin
It actually depends on the boat itself as to whether it's unusual, some companies went thin on the gel coat intentionally , so it's 100% normal, others went with a thick layer of gel, so seeing light would be unusual. it does not mean that the boat is bad, it is either normal for that boat, or just means that a PO may have sanded out some minor scratches on the gel coat.
Gel coat is often applied with a spray gun, so it's normal to see a wide variation even on the same boat.