Dullcoat and any really fast drying solvent paint are subject to what is called blushing if used in high humidity. Blushing is a whitish, slightly rough appearance that does look like frost.
When paint solvents evaporate, they cool the surface. In high dewpoint/high humidity it is easy for a fast dry solvent to lower surface temp below dewpoint, and water from air condenses on freshly painted surface. This water layer has a rough, microbubble appearance, which scatters light making it appear white. Be very careful using fast dry paints in high humidity.