The researchers call it "dream-like" and it is, in the sense that, like a dream, the neurons are stimulated and activated as though sensory input was occurring despite there being no actual stimuli.
Seeing differences at daylight or obscurity while in the womb does not seem impossible. Anybody that has closed the fist over a strong flashlight knows that the flesh is not totally opaque.
Is this dreaming? Maybe, maybe not. Other explanations are possible.