No, the Fiori example you gave is certainly not 'business logic' in my book. What it does is retrieve data (retrieved using business logic on Gateway), you then manipulate that data on the frontend (enter data, maybe do some checks and formatting), and that modified data is then submitted using OData back to the backend, where business logic process it further.
This is not different than any other web application (you may interchange OData with REST, SOAP or a Servlet request/response, and GateWay with a servlet, EJB, CAF, .NET or other web module, or server-side Javascript / HANA XS, etc, but it will always work using the same paradigms)
Furthermore, you don't want to transpose / replicate all your carefully crafted business logic to the browser realm. That would not only be a big performance hog, but you don't want to give less honest people a perfect inside view on how your business logic is set up. There is a perfect reason why you can't directly update a database from a browser anyway 
The purpose of the controller in UI5 is to serve/control the attached view, and not to provide extensive business logic.