Doesn't anyone knock anymore? Seriously, it is a tragedy. Texas is a home is a castle state if memory serves...
He and his ex had an argument, and later he tried to kick down her door at 3am.
Good way to get even less visitation and a restraining order. This is not about gun culture. You can bet if he got the right apartment, that a person does not kick down a door, to discuss custody issues.
If you kick down somebody's front door and bedroom door at 3am, there are likely to be bad consequences in any culture.
Woken up, people are not always at their full sensory capacity. I can see the guy being startled and reacting. A lot of folks would act that way, if they woke up and saw a guy kicking in the door. Who is going to start with asking the guy questions? Not, many, and I suspect that some that claim they would, would be lying.