From what has been said it appears that Miles had previously been riding around with Miller in Miller's car and Miles had his Legal Gun in the car.
They get separated but Miles left his gun in there instead of carrying it around. He then askes Miller to drive over to meet him so he can get the gun in case he needs it.
Miller doesn't have any kind of knowledge that anything definite is going to happen of any kind.
None of it looks or sounds smart after the fact but legally Miller didn't do anything wrong. If he did he'd already be in trouble.
The Tuscaloosa Chief Deputy DA said there was nothing to legally charge him with.
Miller never lied and has cooperated fully.
This is more poor judgement on display but let's not go overboard and make Miller the Bad Guy here. (Not directed at anyone in particular).
That puts an entirely different light on the situation. Unless you read the article very carefully, you get the impression that Miller gave Miles his (Miller's) gun, which Miles then gave to the shooter, and all that took place essentially simultaneously.
Miles leaving his own gun in Miller's car, and asking Miller to drive over so he can get it back, is an entirely different set of circumstances.
Miller is returning someone else's legal property. When Miles asked for his gun back, what's Miller supposed to do....say no?
Note: This assumes that Miller had no reason to expect that Miles or the shooter intended to threaten anyone with the gun upon its return. If Miller knew or had reason to believe that it might be used in an illegal manner, he should have said no.