Caudipteryx is a secondarily flightless bird of the early Cretaceous.
The appearance (shape, morphology) of Caudipteryx clearly shows it to be a flightless bird.
Also, let's consider the feathers. They are symmetrical and do not have barbules. This is exactly like modern flightless birds. See here (chapter 15).
In that light, let's look at the quote from Lawrence Witmer:
" The presence of unambiguous feathers in an unambiguously nonavian theropod has the rhetorical impact of an atomic bomb, rendering any doubt about the theropod relationships of birds ludicrous.” (Witmer 2005)".
This is obviously a dino-to-bird point of view. It overlooks the more persuasive case that the "non-avian dinosaurs" were secondarily flightless birds.