Thanks for the post! Good clarification!
First off let me preface this by saying what someone else said. We don't know all the facts of this incident. We just allegedly know what happened. We won't know all the facts until the security camera footage is viewed and all witnesses have been interviewed. So, no one can make assumptions either way.
That being said... this police officer made several procedural mistakes. He recklessly approached a suspect vehicle alone in a high-risk situation in which he had neither cover nor control. He was outnumbered and had no indication of whether any of the suspects were armed or whether weapons may have been in the car (always assume they are and that there are). Since, he failed to establish any sort of control at that point, he should have allowed the vehicle to leave and called for backup/the local PD, and given them the vehicle description and plates along with the number and description of the suspects he encountered. Yes, you can make the "Take reasonable action to detain or arrest" argument. But, he actually exposed himself pretty badly by doing what he did.
Now, an assumption on my part is that he assumed since they were female and were only shoplifting, they weren't armed. I hope he didn't make this assumption, but his alleged actions say otherwise. Had they been armed and were the type, he would be dead. Too many instances of officers losing their lives in this very scenario or very similar scenarios. There've been several here in the Dallas area.
Moving on. If it turns out that from where he fired he was indeed in danger, it will be a justified shoot. But, if the security footage and or witnesses find him well clear of the vehicle before he fired, he's in trouble. Again, this will all depend on the actual facts not our conjecture here on a forum for geeks. Oh as an FYI, he didn't shoot the driver, he shot a passenger.
While you are somewhat correct about how the officer should've handled the situation (read the above), Skyfrog is correct about warning shots. In the U.S. a police officer is taught to never discharge his firearm in less it is in a situation In which they are justified in the use of deadly force. To put it bluntly, a police officer will only fire their weapon with the intent to kill someone.