As the owner of outpoast, I've explained this in the past, but to summarize:
outpo.st was already taken. Since it was me and a group of frens with an inside joke about building an outpost, I wanted to try to find something where the pronunciation was kept, so we settled on outpoast. Unfortunately, due to my lack of knowledge on the matter, I learned that Poast was a thing, and they don't like us due to their Admin having beef with a guy who helped us spin up the pleroma stuff. In terms of being different? We keep as light a moderation touch on it as humanly possible, and make it a policy to not reach for the defederation button unless federating with an instance is gonna damage our VPS's equipment.