After reviewing the play a couple times, I see why Scott Frost made the call. With only 2 up on the ride side of the kick, the Cornhuskers had a decided man advantage on that kick. They isolated the one defender well, creating a 4-2 advantage.
The issue? The kicker didn't line the kick up correctly. If you take a look again, you'll see he had another 3-4 yards to the left of the defender to use. Had he lined it up correctly, Nebraska recovers the onside. Who knows what happens from there.
As much as I don't like Scott Frost, the lack of execution on the kickers part played a big role in Northwestern's successful recovery.
A risky play nonetheless, and Scott Frost did the right thing in taking accountability as the leader who made the call, but this is something the kickoff unit will have to review during film session. The advantage was nullified with a bad angle.