Delay?

[Scrapper1]

USAV rules at AAU Junior Nationals. I'm R2 in this situation. R1 blows the whistle and beckons for serve. Clearly after the beckon, the team to my right sends a player into the substitution zone. I quickly motion the player away and tell the coach, "No sub! No sub! He's already beckoned".

At this point, the R1 blows the whistle and waves the sub back to the bench. He then immediately issues a delay warning. (Not an improper request.)

Seems to me, the R1 created the delay by blowing the whistle to stop the serve. We could've just played the point and given an improper request at the end of the play. So (1) should the R1 stop play in this situation; and (2) if the R1 does stop the play, do we have to issue the yellow for delay?