Do you need access control? If not, a simple Apache/Nginx directory listing is nice and easy, just drop your files in your webroot and you're set. h5ai is a nice addition if you go that route.
If you need access control (or at least some sort of obfuscated URLs), Nextcloud is a good option. Pretty easy to get up and running, and there's a ton of plugins available.
They do seem to be actively posting in a lot of the communities, so maybe it's just someone trying to seed new Lemmies. There's a lot of people that want new communities but also don't want to moderate, so someone like this could be filling an actual gap if they have good intentions.