Honestly I don't feel like we should worry about which engine they have chosen to use. Unity is a rather robust option these days with some impressive capabilities. There are always upsides and downsides to any of the ready-made engines available on the market. I'm betting they did the research on which was their best option for this title. That's about the only thing to worry over I feel.
If graphics are what you are worried about then I'd say go look up some images of how sharp Unity 5 can potentially be.
