Condensation occurs whenever the temperature drops below the dew point of the air (e.g., fog on a cold night after a storm or near a body of water, moisture forming on the outside of a drink glass chilled with ice, fogging on the inner windshield on a cold morning after you get in and breathe a bit). So, the trick to avoiding condensation is to make the air as dry as possible, or keep the air moving over the warmest surface to prevent the water droplets from forming, or warm the air enough to raise the dew point for that side of the surface.
It's funny they'd take the time to dry out the inside of the light housing with the high beams on (warming the inner air volume), but then not close up the largest openings in the housing to keep the air as dry as possible inside afterwards. Condensation will always form on the warmest side of a surface if the air is moist enough. The condensation reformed afterwards because when the lights were turned off it sucked in the moist air through the housing's openings. Then, when you pulled out into the much colder air, it hit the lens surface condensing the moisture on the inner lens surface all over again. This also explains why driving a bit with the lights on clears the lens. Since heating the air inside the housing also raises its air pressure, I bet if the moisture drain holes had little thin flaps over them, or plugs with one-way flaps in them to let the air out with the moisture and temperature rise, but not back in after the air inside cools down, this problem would go away.
I wonder if a squirt of canned air in the inside of the housing after drying the air with the high beams, then quickly sealing the housing holes would be enough to stop this issue? Sealed beam headlights don't have this issue because the dried air is sealed inside when they're made.