About The Architecture of the project
Architecture of a project is STRUCTURE of various part of the project. Example: A Website can have a 3-tier architecture [FrontEnd->BusinessLayer->DataAccessLayer]. Same way in Automation we define architecture of our project as Test Cases-> Automation Framework->Selenium.
In people have various parts even in an automation framework [Layers]. I faced the same interview question and was able to answer this with confidence and get a job. Thanks to this youtube video where the trainer explained in really well (Sharing the original source link – https://www.youtube.com/watch?v=jwzfshyH9JY&feature=youtu.be&t=749)
To find answer to your question – You can watch only partial video.