Is this actually decentralized? Where's the data backing store?

Until physical infrastructure is decentralized, technically nothing is

Founder @ rivet.cloud + host @ WBRT + advisor @  Dragonchain + helping bring to life a marketplace protocol that can decentralize high-QoS RPC infrastructures

My Farcaster hub is running out of a shitty old PowerEdge in my garage 😁

Yeah. Never had problems with crashes. The server might be over a decade old, so none of the fancy CPU extensions that make it good for compute heavy workloads, but it's got 94 gigs of RAM, so this sort of thing is no problem.