Clemson played terribly.
Clemson's offensive coordinator was precluded from the game as a result of Covid protocol. That would be a hit to offense.
The defense, though, was doing some things that just didn't work (such as not being ready when the ball was snapped).
Also, Ohio State was on in that game, like they usually are in The Game, where Michigan is on the receiving end of such fortune. Many bomb passes that worked perfectly, etc. A lot of that is skill of Fields and the receivers, but some is luck, too. That night was Ohio State's night. Unlike the previous game vs. Clemson, where it went the other way.