I thought it shoots at the closest threat
Negative, Get close enough to a factory and get it honed in on you. Then fly beyond others that are closer. It will continue to target you until someone else gets within a certain range of it.
For example lets say player 1 gets within a 5K radius, puffy ack starts targeting player 1.
Player 1 then extends to 12K radius. Player 2 is within lets say 7K Puffy will still target player 1 at 12K radius.
If Player 2 flys within 5K radius and player 1 is still 12K radius away, Puffy will then start targeting player 2.
Get under 3K of Altitude and puffy will no longer shoot at you (AI Puffy that is)(manned from a CV can still get ya)