"Explain the architecture of your project" checks whether you understand how the parts fit together, not just which libraries you installed. A layered explanation of frontend, backend, database and external services, with one request traced end to end, shows that understanding. Prepare it for every project on your resume and sketch boxes and arrows if there is a whiteboard. Reciting the tech stack is not architecture, because a list of tools does not show how data flows or why you chose them.