Spread is 6.5 but they expect the score to be 21-19.
As you undoubtedly know, the spread is about getting 50% of the betting action on both sides. It really has nothing to do with winning/losing on the field.
Predicted score shows how evenly matched the computer thinks the 2 teams are. Oh, and how inept both teams are on offense in this era of high-powered offenses. If the line was Illinois -2, there would likely be a much higher percentage of the total amount wagered on Northwestern given the recent history of this series.