Having seen it now, I agree it should have been a default. It didn't take an unusual or unexpected bounce in the direction of the ballperson - Brooksby threw it right toward him. Momentary lapse of 'spacial awareness'? Perhaps - he didn't seem to be deliberately targeting the ballperson. But it was reckless negligence.
Just as Kyrgios should not have been permitted to play in Miami after his post-match racquet throw in Indian Wells came close to hitting a ballkid, Brooksby should have been defaulted here for this.
I have no problem with players throwing - or smashing - their racquets. Anyone who plays the game knows that anger and frustration can build up, and needs to be released. But when racquets are thrown, or balls are hit, in the direction of human beings, that crosses the line.
(The ballperson in the Brooksby incident is a man who looks to be in his 40s. I would have loved to see him throw the racquet right back at Brooksby.)