Sometime, when builders wait too long between glassing the inside and outside of a boat, moisture can penetrate the wood on the unglassed side causing it to swell. Since moisture won't penetrate on the glassed side, the swelling of the wood is uneven, causing the wood to warp and making the boat take on some interesting shapes. The opposite can also happen. The wood can dry out on the unglassed side, causing that side to shrink a little. I would think that any problems should be apparent when you actually are able to look at the boat. Look at the actual shape of the boat very closely. Check to see if the sides are pinching in towards the middle too much, or spreading out too much. The rocker might be off a little bit too.

If the boat looks like it's holding the right shape, once you put the inside layer of glass on, it should "freeze" in that position.

It can't hurt to also inspect the visible glue joints. They are normally protected by the glass on both sides of the boat, and if the boat was exposed to very wet conditions in his shop (unlikely) there might be a problem with the glue joints, depending on the type of glue used.

Good luck. Sounds like you might have a find there.