Can a Thin Client be developed in a multi-tier architecture?

I am trying to determine the of architecture my system.

The book: Sommerville, Ian: Software Engineering (9th Edition). Pearson 2010.

says that a thin-client is a two-tier architecture.

A thin-client model, where the presentation layer is implemented on the client and all other layers (data management, application processing, and database) are implemented on a server. The client software may be a specially written program on the client to handle presentation. More often, however, a web browser on the client computer is used for presentation of the data.

Example of a thin-client from the book:

And he talks about multi-tier archtectures as well:

"The fundamental problem with a two-tier client–server approach is that the logical layers in the system—presentation, application processing, data management, and database—must be mapped onto two computer systems: the client and the server. This may lead to problems with scalability and performance if the thin-client model is chosen, or problems of system management if the fat-client model is used. To avoid some of these problems, a ‘multi-tier client–server’ architecture can be used. In this architecture, the different layers of the system, namely presentation, data management, application processing, and database, are separate processes that may execute on different processors."

Example of multi-tier client-server architecture from the book:

However, the article: Renzel, Klaus and Keller, Wolfgang. Client/Server Architectures for Business Information Systems. 1997.

Has the following figure:

And says that the Remote User Interface is also knwon as a Thin Client.

I am trying to put this information in context with my own system. It consists of a frontend and a backend which communicate together through a web service. The user interface (frontend) only presents data that it requests from the backend, where all all major logic is implemented. The below figure is my system architecture:

The frontend, backend and database management system could be implemented on seperate severs if necessary. I chose to put them all on a Windows Azure Virtual machine. Is it a Thin Client or not?

I would argue that it is because the presentation layer doesnt do anything special other than present data (and sometimes post) to/from the backend. But it is not a two-tier architecture as Ian Sommerville says that a Thin Client should be.