Can Someone Please tell me if This's bug or What, How did he got exuted and not kill ?

Before i entering to the discussion, Please not Judjement on rank or skill level of Video. Thank You After i killed This heimer With miracle consider how broken That champ is, Lee sin was top and i tryed to outplay him ... i dont get Why He got exuted Because i spent like 10 seconde in combat with lee sin, I intentionaly Q that minion and not vital So i can hit lvl 6 and run away with movement speed from ult. After i run away and he tryed to dive me. I parryed his Q or rather W his q for those Who doesnt kn fiora w name... Parry was suppose to do damage to him and block spell Yet he got exuted. I honesly almost lost my mind after That play and near deleted This game. Please Someone explain to me how the fuckk he got exuted and its bugged and i missed Something ? Whats even triggering to me is that i been getting +20 +21 all day/win and i got +19 That game, im 99 lp now