Do you have any pictures showing higher up on the boat? That doesn't look like osmotic blistering. The texture of the surface itself doesn't look like gelcoat. What that looks like is white bottom paint. Yes, they actually make a white bottom paint, my neighbor in the winter yard has a go fast boat with white bottom paint on a white hull.
What I see in your pics looks absolutely like a bottom paint in which the previous coat was not properly prepared, and is now peeling. Notice that the layer below it also looks like the same eggshell/orange-peel texture and color.
Bottom paint delaminating is not the same as osmotic blistering.