“Having no obligation to flee does nothing to establish that a threat exists. “
It only takes a fraction of a second to have a threat exist.
Which is true every day, everywhere you go. Yet you can't go around blasting people.
A threat must be objectively reasonable and imminent, not imaginary or projected.
As soon as he left the house the immediate threat was over. He then had the opportunity to call the police and stay away from the intruder. By returning he re-initiated the confrontation and forfeited any claim of self defense.