delay of game warning or not?

[Air JC]

My partner made this call...

A1 scores a layup from a half court set. Many players are in the lane at the time.

As ball passes through the net, B1 slaps the ball (not too hard, but obviously ticked off that she got beat on D)

My partner gave B1 a delay of game warning. I have never seen the warning called this way, what do you guys think about calling the delay warning on the team about to inbound the ball?

Other officials have told me that my partner should have just started the 5 count when B1 slapped the ball since it was at her disposal.

There is not a great deal of room in this gym, so it's not like the ball went flying far away from the baseline, but in a large gym, the ball could roll very far away in a situation like this. Do you start the 5 count? Call time until you can place the ball at the disposal of team B? Or call the delay of game warning (or T, if 2nd violation)?