The first question would be why was the partnership income not reported on the FAFSA- is it something as simple as you following the line by line instructions and not seeing it asked for anywhere? If so, then perhaps it should have been on the woksheets.
If this is an honest mistake, make sure they know that, ask the person how it should have been filled out. The forms are complicated and confusing, and they adjust them a bit each year. I have made errors several times online, usually to my deteriment, by entering info twice, getting confused when it pops up screens asking if I am sure about the numbers, then entering the same info both in the student place and the (non existent) spouse place.
I have not actually heard any stories on this forum until this spring relating about people being asked for bank stmts. If it were me, I would call the person, let them know I am concerned that since they are digging deeper I must have made an error, ask them for input. If you were honest and truthful and made an obvious and easily explainable mistake, they probably won't fine you, but I would expect them to go back and recheck the prior FAFSAs and they may adjust aid due you to be correct.
Did you or your parents complete the form?