Since you’re doing it for free/the experience, I don’t think you owe any explanation other than, “Okay, I’ve finished the edit. Here it is.”
If he has questions, etc, though, this might be valuable feedback for you about the aspects of the edit that worked best and so on. So if he has them you might say something like, “Right now, I have other obligations [I always have “other obligations”–it’s a very useful phrase] and can’t continue to work for free but I would be happy to have a quick phone call with you [“one-hour call”; “half an hour on Zoom”–whatever suits you] to discuss your feedback on the edit and to answer any questions you may have about it or about the process moving forward.” Putting things in clearly defined containers helps a lot.
If he says something nice, ask, “May I use that as a testimonial?”
Don’t forget, you’ve done a monster amount of work for this person for free. You’ve done him a favor, not the other way around.
Setting and holding boundaries is one of the biggest challenges we have to deal with.