just a quick look through wiki its more accurate then you might think.
last win over a ranked team was 2021 vs #4 Penn State, ISU was earlier in the year and somehow Indiana was ranked to begin the year (finished 2-10). All three of those teams ended unranked at the end of the year. you have to go back to 2019 when they beat MN to find a team they beat that was ranked at the end of the year.