what is this interview for?

make a timeline of your employment history/education and address. Make sure you can properly answer Employment based questions like job duties ,what you do day to day? Interview usually depends on officers, often they go through your application form and ask if they want to verify anything.

is this part of EAD process?

this is for i 485 interview

one of my friend had it some time ago , if you have dependent (spouse) who you added during the process then they will mostly ask you questions regarding marriage. else it would be yes/ no questions mostly that’s what he told me! Goodluck 🇳🇵

yes i did add my spouse during my pending i 485