Why did Arun Gawli get angry with Phamplet Bandya?

In the movie Daddy (2017), there is one particular scene where Arun Gawli (played by Arjun Rampal) asked a child about where he came from, while his man Phamplet Bandya (played by Deepak Damle) was recruiting children in their gang.

The scene goes like this:

Arun : Kuthun Aalayas? (Where are you from?)

Child : Dharavi.

(Arun gets angry and slaps Phamplet Bandya.)

Phamplet : Mistake zaali bhau (I made a mistake sir.)

(Arun asks each of the children about where they come from.)

Why does Arun ask children about where they live and why did he get angry with Phamplet Bandya? Is it because he only wanted to recruit children in his gang from Dagdi Chal (where Arun is living)?

Or is there any other reason behind that, because in the next scene we can see that same child doing target practising?