Koda,
Friendly AI ack can hit you when it's firing at enemy planes. It's not trying to target you, basically you flew into it's stream of fire. Go offline, to a CV, then take off and come around for a landing. The CV's guns will be firing at the drone P-51 "enemys" overhead. As you land the ack on the end of the CV on the port side will very likely hit you as it's firing at the P-51s. If you try the backup trick on the flight deck in a large plane, you probably will be hit by the CVs ack.
The puffs around friendly planes when you're in the mannable CV guns is your near hits on them. However it does no damage to them because the system reads them as Killshooter hits, as if you shot them with a plane's guns. And I've never been killshootered while in a mannable CV gun, so apparently it doesn't count those.
You didn't see the puffy ack of your own mannable gun around the enemy plane because you weren't close enough in accuracy for the enemy plane to take a hit from your proximity fused shell. Remember, if the enemy plane is under 3K, the CVs puffy ack will not be firing at it, so there won't be any puffs of ack near them but the ones that are from your mannable gun proximity shells.