The interview takes a form of a panel discussion, 3-5 team leaders first introduce themselves and then present the project/team they're working on/with, day-to-day tasks, project goals, what problems is the project trying so address and why, and if the project is just a stepping stone/base/building block (typically a library), then which products from the portfolio use it and how these interact with it (only briefly though).
The interviewers then approach the candidate with questions targeting the candidate's technical skills (this follows the technical skill and knowledge base on-site test, the results of which of course had served the decision process of further interviewing a candidate).
Lastly, the interviewers ask the candidate whether there's any intersection between the candidate's interests and any of the presented projects, thus indirectly asking them about any preferences.