defense.   in most (not all) cases, when an offense commits a foul, it creates a dead ball situation that in every case negates a score, and in limited cases only  brings the ball back from the spot of the penalty.  When defense commits the foul, the score counts, and all that.

You are arguing a scenario in the rules that is not the same fact pattern.  The scenario in the rules in the NCAA online rules section says that if the non-player comes up to a celebrating teammate who already scored, the score is maintained, and the penalty is assessed on the following play.  That's not what we have here.  We have a live play, ongoing, with the non-players going onto the field of play.  Since the KR was in progress, that would mean they are the offense, and it should be a dead ball foul.  I don't see how you get to the point you're getting.  Later in the rule, for example, you have this example, which is the closest I could find of all the scenarios outlined in there, even though it involves a live player:

"Back A22 takes a backward pass from the quarterback, circles right end, and heads for the goal line. Guard A66, who had pulled out to lead the play, legally blocks B90 to the ground and then stands over him at the B-30 taunting and screaming obscenities. This draws a flag from the head linesman, when A22 is at the B-10 before continuing into the end zone. RULING: Live-ball foul for unsportsmanlike conduct. Fifteen-yard penalty enforced at the spot of the foul, which is the B-30, and repeat second down. Second and 10 at the B-45."

I don't know, I see what you're driving at, but it doesn't seem correct, and frankly there is no directly on point example reflected in the online rules.  I'd accept an actual NCAA rules expert opinion on this.  Has one chimed in yet?