If we believe what we know of his explanation his life was in danger, he was being physically attacked by two 17 year olds. Neither article address' the legality of his handgun, given the lack of charges I presume he had an FOID, required in IL else a felony on it's own, and perhaps a CCL.
I suspect his biggest problem is the several day time delay between the theft and confrontation and his attempted recovery of the car personally rather than calling the police and telling them where the car and perps were.
And there's a lot we don't know. His background. Any possible relationship between himself and the theives. How he knew where to find the car and theives. And whether there's any video or even witness'.
Personally, particularly when armed, I think it's a mistake to insert oneself in an unnecessary confrontation. He had other options. But in itself, I don't see how that's a crime. In fact unless there's something significant we don't know yet I don't really see a crime here.
Does not matter what you and I believe.
The law specifically prohibits playing cop.
Texas gives a little more leeway to those who wish to protect their property from theft, but the law in most states forces the victim of theft to stand by while the thief carries his TV, silver and whatever else out of the front door.
Once the thief turns his back on you and attempts to leave, you become the lawbreaker if you take any action that results in serious injury or death.
Anyone who carries and does not understand the law is very likely to end up in prison.