If you are using 0w-20 and Atlas Honda are themselves pouring it, then no need to worry. GOD Forbid, if anything bad happens with the engine due to 0w-20 engine oil grade (which is highly unlikely), then they will be responsible, and handle and manage warranty issues themselves.
I personally think, 5w-30 is a very well engine oil grade for Honda City, and one may use it, however, if everything is in the hands of dealerships, and they are poring in 0w-20, the vehicle is under warranty, then let them be responsible for everything.