do you know for a fact that is him and not just someone using his name? either way this is fairly harmless

using a meshVPN like tailscale or netbird would another option as well. it would allow you to use proper backup software like restic or whatever, and with tailscale on both devices, it would allow restic to be able to find the pi device even if the other person moved to a new house. (although a pi with ethernet would be preferable so all they have to do is plug it in to their new network and everything would be good. if it was a pi zero then someone would have to update the wifi password)

a “poor mans” backup can be useful for things like this, movie/tv/music collections, and will only be a few MB instead of TB.

if things go south at least you can rebuild your collection in time. obviously if theres some rare files that were hard to get then you can backup those ones, but even at that it will probably still be a small backup