Why the full-toss bowled by RR against DC was not referred to third umpire?

While there were many who criticized the umpires for their poor decision after Delhi went on to lose the match by 15 runs, the on-field umpires were indeed following the rules of the game by sticking to the rule book. As per the IPL Playing Conditions, the on-field umpires can only refer a decision regarding a dismissal and front foot no balls to the third umpire and no other referrals can be made apart from these.