"A person is justified in using
deadly force against another to protect his property to the degree he reasonably believes the force is
immediately necessary to prevent the other's imminent commission of arson, burglary,
robbery, theft during the nighttime or criminal mischief during the nighttime, and he reasonably believes that the
property cannot be protected by any other means."
I believe this is the standard in use in Texas. The application of deadly force isn't the same as the threat of force, but this should give you an indication of what questions need to be answered before firing.
Is a person walking towards you while talking on the phone a threat? On its face, no. Granted, your senses perceived that something wasn't right, & you probably were correct. However, if guy had cringed in fear and ran into the store to call the PD, you'd have some problems.
The "property cannot be protected by any other means" could put you in a jam. Could you have entered your car? Walked away? Trotted?
Pulling out your gun worked in this case, regardless of the guys intent, he left. However, if he had continued to walk up to you, what would you have done? Shoot an unarmed guy talking on a phone? There's no clear intent to commit a crime. The girl would have told the PD that "joe" was asking you for a cigarette or a dollar and you shot him down...
Your behavior should be subjectively and objectively reasonable. Just because you thought something was going on, would another reasonable person reach that conclusion? You will be judged by a "jury of your peers", and I bet none of them CC.
Just giving you the conservative answer, so you can work on your tactics. Start with verbal commands "Don't come any closer!" "Stop or I will shoot you!", something along those lines. Can you escape? Make an attempt to do so...a few steps, something. The guy is 25 feet away, get around the other side of your car and keep it between you.
These scenarios have plenty of answers, some right and some wrong & some that are "more right" than others. You lived to fight another day and probably don't have an outstanding warrant, so it's all good