Maybe I have misunderstood your question, but when iOS asks for permission to know your location to access photos, it's the location in the photos the ask for. Since the location is stored inside the photo as all other EXIF tags, I believe Carousel requires this in order to not strip away any metadata from the photo
What you are seeing is the standard "location services" permission request from iOS, and you'll see it in other photos apps, too. The text is provided by Apple, and it's meant to inform the user that if your photos contain location data, the app that you grant access to will be able to see the location data in photos you import. This is completely normal for any app that imports photos. Unfortunately, the text in the alert is misleading, as it suggests the app actually wants to track your location. Please rest assured that Carousel does not track your location, nor does Carousel have any interest whatsoever in knowing your location! In order for Carousel to let you import photos, it has to be granted permission to read from your photo library.
-Sumner Paine, product manager