yes its gelcoat, unless its been repainted.
when they mold the body they first spray the finish coat, (gelcoat) on the inside of the mold, then lay the fiberglas over that. sort of backwards to what logic would tell you to do.
if you want to learn about, and do repairs on or refinish gelcoat i would go to the library and read about painting
and refinishing fiberglass boats. same stuff except you don't have to lay on the ground underneath it as much. and boaters have a long history of screwing up gelcoat so have a lot of info on how to fix it. plus the products to use.