EDIT: NCAA Rulebook explains why INT return was a (EDIT 2) Mess

"Ball carrier A33 is running toward the Team B goal line. He drops the ball just inside the one-yard line and, thinking he has scored a touchdown, circles through the end zone and runs to his team area. There is no touchdown signal by any official. The fumbled ball hits the ground just outside or just inside the goal line, rolls along the ground in the end zone, and is declared dead there when it comes to rest and no player attempts to recover it. RULING: Touchdown. The ball belongs
to the team last in possession at the dead-ball spot. By definition an awarded fumble in the opponent’s end zone is a touchdown. (Rule 7-2-5)"

Found on Page 45 of the Rulebook


Rule 7, Section 2, Article 4, Subpart c

c. Behind or Beyond Goal Line. When a fumble or backward pass goes out of bounds behind or beyond a goal line, it is a safety or touchback depending on impetus and responsibility
(Rules 8-5-1, 8-6-1 and 8-7) (A.R. 7-2-4-I,
A.R. 8-6-1-I and A.R. 8-7-2-I).

Now to "impetus and responsibility". We have a rule for that.

Rule 8, Section 7, Article 1

"The team responsible for the ball being out of bounds behind a goal line or being dead in the possession of a player on, above or behind a goal
line is the team whose player carries the ball or imparts an impetus to it that forces it on, above or across the goal line, or is responsible for a loose ball being on, above or behind the goal line."

and Article 2, Subpart a

"The impetus imparted by a player who kicks, passes, snaps or fumbles the ball shall be considered responsible for the ball’s progress in
any direction even though its course is deflected or reversed after striking the ground or after touching an official or a player of either team"