Not CPS worthy unless there’s a significant (and I mean SIGNIFICANT) backstory or the child gave a disturbing explanation like this gun/knife and tree set up is happening in his/her backyard and they play back there. I’m guessing something had to have been said for someone to call over a child’s drawing.
Personally i think they should of contacted you first and had a meeting with him and you together. They know about your son (not meaning that in a bad way)
I would only be concerned based on the child's explanation behind the picture. I wouldn't jump the gun on calling cps though...I would be concerned if the child was exposed to violent things or perhaps saw something on the news and exhibiting anxiety.
No. Not at all. I would only be concerned if there were other concerning incidents before or leading up to this. But if its just this picture then absolutely not