Yes, they are totally different from free-form art. They're coloring in someone else's art instead of creating art. In comparison, it's hard to understand how using simulated soldiers some of the time, instead of molded plastic ones, is supposed to be so harmful to imagination.
I don't really see coloring books to have anything to do with art. I wouldn't say a child coloring in a coloring book is making art or experiencing art in any way rather they are most likely having fine motor practice while they wait for the entree to arrive at a restaurant.
It sounds on the other hand like people were suggesting that playing a video game is a way for children to have experiences or develop imagination. As in how would kids have the experience of combat or civilization building without them. My answer is that children for generations have had these experiences by using imagination and by creating with self created stories.
It has also not been my observation that coloring books are an activity that most children engage in for hours. I'm sure there are kids who have, but unlike screens they tend to be a pretty self limited activity for most kids.
