It is obviously true that you need moisture for ice but it does not have to be above the freezing layer. If your temperature gauge is showing a very low temperature but not quite freezing, say 2 degrees, then you can still get ice. When it gets very cold and high you tend not to pick up ice even in cloud but that also depends on the cloud.
You can also pick up ice hitting freezing rain which has happended to me once and I do not care to repeat it. This was also slightly above zero but the airframe was still very cold from a descent.
Just because an aircraft is "Cleared for known icing" does not mean that it is a good idea. Small amounts of ice from passing through cloud layers to get on top in a non de-iced aircraft can be acceptable to many people whereas severe icing to a de-iced aircraft can still be very serious.