Because there were survivors - no hope in water against 11 remaining super trained pilots of attack aircraft that are hyped up , and where no quarter is expected or given , on both sides - I am sure they observed something astonishing that appealed to the air leader's honour code and so ordered leaving survivors as witnesses or out of tribute , but is only conjecture - but could have been 11 armed aircraft shot at and missed sailors floundering in the ocean during sustained attack without return fire post ship sinking.....or the Zero's were low on fuel ( 2,600 km range)
Here you go - some fact (given the RAN hasn't edited it out) -
As the soldiers and sailors began to evacuate into the water, the Zeroes stopped attacking the sinking corvette and began strafing runs on those in the water.[14] Ordinary Seaman Edward "Teddy" Sheean, who had been wounded in the initial attack, strapped himself into one of Armidale's 20 mm Oerlikons and opened fire on the aircraft.[14][15] Teddy forced one Zero to crash into the sea and damaged at least two others; continuing to fire until he went down with Armidale.[14] Low on fuel, the Japanese aircraft headed for home.[14] The survivors found that the two ship's boats survived the sinking, and were able to fashion a raft from debris.[14]
https://en.wikipedia.org/wiki/HMAS_Armidale_(J240)
I doubt bushido came into it - that was a samurai code, and fighter pilots were unlikely to be samurai.
