Laminating is the process of "gluing" the fiberglass to the foam with resin. It gives the board strength.
Hotcoating (or seal / sanding coat) it the process of applying resin with a brush on top of the fiberglass lamination to seal it from water and also providing a resin surface that can be sanded smooth.
The term "hotcoat" is an old term referring to glassers adding a lot of catalyst to polyester resin to make it cure fast. The resin heats up when curing and the board would feel warm - therefore a "hotcoat"...Today with the popularity of epoxy resins, the term seal or sanding coat is more accurate and pertains to all types of resins.