That is horrible if true (I find it hard to believe that US military personnel is trained to use "tactical" hand signals when trying to communicate with the general public).

However, it says that the policy is to first hand signal, then fire warning shots, and then they are authorized to use deadly force.

So, if these killings are because people don't understand hand gestures, and assuming policy is followed, they also don't understand warning shots, which seems like a stretch.