It isn't a lucid dream. You are not aware that you are dreaming, but what you come up with in the dream will turn out valid. For instance, in the dream you figure out something, write a poem, do some math, or experience something (such as the Beethoven and Mozart pieces I quoted in my Iris Chang post), and they all turn out valid after you wake up.
Sometimes the experiences in the dream are more focused and poignant than their counterparts in waking hours.