Someone likely used something to strong in a pressure washer and damaged the paint at some point.
A buddy did that to his Lowe. There was a stain from cedar water along the water line and he used his pressure washer with what ever mildew remover he used on his house siding on the boat. It likely had bleach or something super aggressive in the solution and it ate the paint. Castrol Super clean stripped the paint off my old Grumman years ago, I had used it to clean the garage floor, and the boat was pretty nasty after one trip so i just diluted the mix by half again and went at it. I went over it with just water, let it soak a bit, then I hit it with the soap, let it soak about 15 minutes, then went back with high pressure water. The paint on the inside looked like had worn away and it was flaking off paint from the lower hull. The Castrol Super clean had turned the paint yellow with cracks all over, when it dried, the paint was just flaking off. I just kept cleaning and ended up repainting the hull the next weekend with fresh paint. To be fair the paint was 24 years old when it happened but it wasn't falling off. In a way I lucked out because as I was prepping it for new paint I found corrosion in the transom and I ended up replacing the transom wood and finding that they had used pressure treated wood that was eating the hull. If I had left it, it no doubt would have gotten far worse in short order. I was able to neutralize the corrosion, patch the damage and seal it up and all was fine.
Monark boats, in the later years were the same as Starcraft. That boat looks a lot like my 1999 SF14LW hull but with a console.
I've always found the Starcraft hulls very corrosion resistant. I've used mine mostly for crabbing and its never shown any signs of corrosion. Mine is rated for 35hp max. (The original brochure listed it as 30hp, but the CG plate reads 35hp).
Starcraft paint is also pretty tough, when I bought mine, the original owner had painted the registration numbers on each side and had moved with it through four states before he sold it to me. I used lacquer thinner and 0000 steel wool to get the old numbers and layers of white house paint off in between each set of numbers and the paint came up perfect once it was all gone. I then hand lettered it with my numbers over the original surface. My guess was that they used some sort of powder coating and not solvent based paint but I can't say for sure but the lacquer thinner and WD40 and Goof Off I used didn't phase it.