[Gameplay] Yasuo's shield is triggered but he gets "executed" instead killed

Played a game as Poppy against Yasuo in mid lane; he towerdived me and killed me, i hit him and activated his passive shield, however i did not fully broke it so his health did not get damage from me, and when the tower killed him i did not got the kill - he got "executed". Maybe this is intended for his shield however i do not think it should be like that - i could have escaped but i stayed to trade kill for kill.