The expansion of the NZ - in HS football - has no other significance on scrimmage Kicks other than to allow for normal line play - including the tipping (which would be ignored) of a low kick by R while in the ENZ. In your question, if the RT goes downfield without blocking anyone he has committed no foul.
It is important to note that the ENZ immediately disintegrates when the kick crosses it In this instance, if the kick somehow returns behind the NEUTRAL ZONE (not the ENZ) K may recover and advance. If R has muffed/touched the ball beyond the ENZ or K's advance reaches the line to gain, K is awarded a new series.
However, if K recovers within the ENZ, they may not advance it. In this this case, any new series for K would be determined ONLY if R touched the ball beyond the ENZ
See 6.2.6 Situation