Same issue that you described qatherine.
MAC OS 10.13.2 High Sierra
Phone OS 11.2.1
Not a user of iCloud, and my devices have all auto syncs off. No external file storage. And no sharing between MacBook and phone enabled.
Got new iphone 7. Emptied trash on old iPhone 6. Backed up 6 through ITunes. New iPhone 7. Restored from iTunes.
Now? 8,000 photos in my deleted photo folder on my phone that were not there when I synced my phone for backup for the sole purpose of moving data to new phone. Many of them are from YEARS ago that I know were not saved, I and were deleted at the time, and as my iphone 6 has not been backed up since I got it, I cant see how any of those photos would have been still around when many were deleted years ago. I am also a person that monthly empties the Deleted Items folder on my phone so I dont use up all that space, so yes I am sure they were deleted.
Now I am wondering if they ever really were deleted.... and why bother deleting the deleted folder if they dont really go away? And does that mean that if I now delete these 8000 photos, they will be back again?