It means the humidity was high.
No, not trying to be a smart a$$ but the reason is that as air is drawn into the engine through the intake it is cooled by the effect of passing through a narrow space. It drops below the dew point which can cause moisture in the air to condense on the surface of the manifold much like it does on the outside of a cold glass of ice water.
This is why airplanes have a method, (carburetor heat), to keep that moisture from freezing and blocking the carb. On a car or a motorized bicycle, no big deal, but in an airplane if the carb ices, you'll be looking for a place to land, real quick. This is an oversimplication of why the intake manifold gets cold but suffice it to say that it is simple physics. And, it's normal.
Tom
