From my point of view
Project Architecture means what are the tiers in your project with flow diagram.
suppose your project contains 5 tiers like client tier, presentation tier, Business tier, Integration tier, Data tier, then you should draw the all tiers flow before the interviewee if required. Project Architecture is nothing but is the structure of your application. What are the layers are used to retrieve the data from the Database.
I made a short project on J2EE that contains my Database Design, Application Layer, Connections, User Design Diagram, Data Flow Diagram. You can explain the interviewee by your own diagram if you can explain your project, although assuming you are not perfect in drawing.
