If you check the pool you will see the images are different.
Actually see someone parented them, correct me if I'm wrong but arent we not supposed to do that if the 2 images are already in a pool? Just curious since thats the reason I didn't.
If the images are sufficiently related there is no good reason not to parent them, even if they are in a pool.
What you may be thinking of is that the previous way of "pooling" was to just parent all the pages of an artbook or such to its cover image. That's what's being discouraged now that we have proper pools to work with.
