Wrong team tries to throw in after basket

[Art N]

I had this twice last week in back to back girls Fresh/JV games.
A scores and B seems to be taking their time or confused about who is suppose to throw the ball in. A1 steps out of bounds and grabs the ball to throw it in. My partner T doesn't do anything, so I blow my whistle and issue a delay warning on A. Should this have warranted a T? Should I have eaten my whistle and let him ignore it? I can't find the reference or case in the book in a quick scan. Thanks for your input.