Yorick Damage Error in Match History?

After playing this long, exhausting match, I decided to look over match history and... well, while the enemy Yorick was certainly formidable, he just CAN'T have done 1066.2k damage (including around 1000k true damage) to champions, when the similarly fed Katarina did 56.7k to champions. Is this a bug or error with match history or Yorick? Unless Yorick's ult ghoul "deals damage" to itself when it expires?