That's close but not quite right. You're right that colder air has less capacity to hold moisture, but when you lower the temperature of air the RH goes UP (not down). As you keep lowering the temp, at some point the RH reaches 100% and then you get condensation. That's why cold beers 'sweat' when it's hot and at least somewhat humid: the air very close to the beer glass reaches 100% RH (because it has been cooled by the beer glass) and the moisture from the air condenses on the glass. It's also why cold fronts often cause rain. Also explains why we often have static and humidity problems when it's cold (because we are heating cold air, which makes the RH go down).
If your humidor was at; say 80* F and 70% RH, and then you chill the entire humidor relatively quickly, at some point you'll have water droplets (or at least a fine mist on the walls) inside the humidor because the RH would reach 100%.
EDIT: and just to add one more thing, RH is dependent on temperature as well as the moisture content of the air. Dewpoint, is purely a measure of the moisture content and is independent of temp. Of course, dewpoint is given as a temp which kind of confuses the matter.
