How did you send the the file to the laptop. Editing in Photos is non-destructive, so even though you've cropped the image it's still all there and can be reverted to the original. When you save/send a file it will try to preserve the original file if it thinks it should, and only send the edited version if not.
Needless to say, it doesn't always guess right.
Sending things by email or through the web almost always sends the modified file. Saving it in a way that goes from photo/video editor to photo/video editor tends to keep the whole file. Going through different platforms is unpredictable.
All I can suggest is trying a few variations on how you share the file from Photos.
I was able to get a modified file out of Photos by saving to the file system on the iPad. When I re-imported it to Photos all I got was the edited video.
Or, you can use iMovie or a third party video editor to modify the video, then export it from there.
