One of the most basic rules of marksmanship is know what you are shooting at and be sure of your backstop (what your bullet will hit if you miss or your bullet goes through your target).
If you are shooting in the air you have know idea what you are shooting at or where your bullet will eventually come to rest.
I have read of many tragedies caused by hunters and shooters who did not follow these two simple rules.
I agree this man had the right to defend his home but he did recklessly fire his rifle in the air. He may be guilty of reckless endangerment of his neighbors.
For all you and I know...the guy had blanks!
Do we know he was arrested for the air shot and not for firing, period?