As Kaiba slowly descended into unconsciousness before finally dying, he murmured "protector... o..... sa...nct......."
He truly believed he had won in his final moments.
This was the most important thing about Kaiba's death. Believing he had won, he allowed himself to sleep into the shadow realm.
N E V E R T O B E S E E N O F A G A I N
It was a well fought match, but in the end Yugi won, and Kaiba ate shit.