it has to do with the heat sealing the windings in place on the coil forms...The Champion manual also mentioned that varying the load also thermal cycles the stator windings. Not sure why that's needed. Maybe one of the generator gurus knows why that's beneficial?
most of the gens are not test ran, so the coatings are not hard yet.
so a bit of warm to start baking the windings gradual is a good thing.