It's possible for parts of an app to be decentralized and parts not. With Steem, most people really just care about the decentralized reward system (or really they probably just care about the reward system which happens to be decentralized, but that's beside the point here). So D-Live was a centralized app which utilized the Steem decentralized reward system to reward the content.

I think that is totally fine, and would like to see more apps use that model (vs the dtube model of trying to fully decentralize everything and having a poorly working product as a result).