Each time the engine cools down, any humidity condenses on the interior walls of the motor. Next time the engine heats up it turns this water to steam vapor IF the engine is run long enough and gets hot enough.
Further, there is a breather element filter at the bottom of the filter box that must be periodically cleaned/cleared and reinstalled for the engine breather system to work properly. If it clogs, you get more condensation buildup in the engine. Addressing this, is part of the routine maintenance schedule, but seems to be frequently overlooked.
Cheers,