That seems like an unusually high kill count on that plane. Maybe the number of successful bombing runs?

It is a Zero so that is the kill count.

"unusually" You might want to check how many planes some of the Japanese top aces killed.

Also AII- with two red bands are Kaga's aircraft, she also never had Zero Models above 21 IRL so this is our Kancolle timeline.

This is how our fully Aced A6M squads in Kagas slot would look like.