Basically HR email you to fix the interview and to fill up the application form and submit the documents prior to it. On actual day, you will have to contact the other HR staff and will be brought to their common work space where I felt they lack professionalism as they were discussing lunch plan when there public around. The hiring basically asked questions beyond what a normal interview will ask. Like post a real life scenario question and wanted an answer from the candidate which shown they lack the professionalism as question like this should not ask candidate during interview as end of day they get free solution to problem which their level of seniority they should be able to address