“He would have had to have known at the time that the boy had been invited into the house in order for that to matter. Since the girl lied and said she didn’t know the boy, that was the knowledge the dad had at the time of the incident.”
He had to have a reasonable belief that the boy was an intruder. It’s probably going to come down to whether the grand jury thinks that, under the circumstances, that would be a reasonable belief.
Trust me, in Texas the fact that the boy was in the house, was unknown to the father and the daughter claimed he was unknown to her is all that the grand jury will need to hear. I agree it would be different if he had met the boy before, etc. But at least in Texas, it is perfectly reasonable to presume anyone in your house under the circumstances as described in the story is a threat.