Imo it’s hosting stuff for yourself or your family. In cloud or closet. If you have an advanced nas and you set up shares so everyone in the house can use it, it’s self-hosted storage. If you set up an iCloud account its not. If you rent vps, manage firewalls and reverse proxies and host your stuff there it’s selfhosting. If you use digital ocean or aws and do it for yourself its selfhosting. Saas isnt self hosting

I do like it though and we ran a cluster for lab at work for a year or so

Linux knowledge is broader, especially since truenas went core. For most enthusiasts Linux gives more Google answers than bsd ones. Also the gui is harder to install for non paying users. Linux is even got gamers these days