I thought when you used a ~le word as an adjective, it followed the noun. Shouldn't "That book" be kitabu kile?
In this sentence, kile ni kitabu changu, kile is the subject alone and the word "book" is in the complement. It means "That is my book" not "That book is mine."
I think so too.
"That book is mine" feels like "Kitabu kile ni changu".
In context, it might make sense this way if you were differentiating that book from others.
That is my book