Not “fully-owned” though if you need external services to do the heavy lifting. I think they mean deployed onto a personal vps.
Two of which are services operated by a corporate entity and one of which is a closed source piece of software.
The only thing "owned" here is the fact that the entire blog is simple markdown and the domain name. However, that doesn't mean it's very portable. It's not impossible, but it's a lot more work than I would want to do.
It's not really fully-owned, but it's owned in the ways that matter most
The internet as a whole relies on a huge variety of services all working as they should.