There was a kind of question or confusion I always had with the definition of what is an app (now called add-in). Also this confusion happens to me because of the name changes.
You can have two types (SharePoint-hosted and Cloud hosted).
And when you create a custom list through the UI you select the option Add an App you are using the Sharepoint-hosted app.
According with the newer definition.
But how can they have an ASPX pages and can just have code that is possible to be executed on the browser only, according with the old definion ?