If an app only has one user, it doesn't need to scale, it needs to perform. Scalability is all about users and only loosely related to performance. Datasets are irrelevant.
scalable - How well a hardware or software system can adapt to increased demands.
scalable - the ability of a product or network to accommodate growth
The ability to scale hardware and software to support larger or smaller volumes of data and more or less users.
the ability of a computer system to shrink or grow as requirements change