Dream characters are people that you actually saw before in waking life, maybe in TV or anywhere, even if you don't remember them.
Not necessarily true. The facial features we have seen throughout our lives can be tweaked/used to create a new face we have never seen before. For example, I'm sure everyone has drawn something at some point in their lives. Maybe we wanted to draw a whole different species, or perhaps a new character or person, etc. Whatever it may be, we most likely used features we have seen or experienced in life as a reference, but we know we can modify those set of features and arrange them in a way that makes for a completely new design constructed from within our own creative imagination. I could go out and create a face that has the lips of my mother, the hair of my best friend, the nose of my grandfather, and so on and so forth. The face that I will come up with won't necessarily be of someone I have already met before in waking physical reality. Not only that, I can go more specific and modify each and every facial feature I have added, maybe stretch the nose here, or make it bigger, or color the hair differently, add some wrinkles here and there, stretch the face, make it skinnier or fatter, etc. I can be even more creative and add a few more eyes to said face, or maybe add some wings to my character, some horns, different skin color, height, width, etc. There is no limit to what we can do.

True inspiration is a more complex idea, for we always require something as a reference from which we can use to expand and devise something entirely different. Still, a DC I may see in my dream don't necessarily have to be someone I've met before in waking physical reality.