Wrong death recap

I'm lately playing Sejuani as my main jungle tank. Im building around 4000HP late game. But I'm very suprised when im getting killed sometimes very fast (i guess opponent team focus a lot over me) but even if my HP is not going low fast, most of the times the death recap is totally wrong.

For example, im sharing a link where I get 1000 or 1600 dmg in 1 second (this was a towerdive in midgame), but neither the killer or the 2 assisters do more than a total of 400. Even if it was cs who made most of the dmg the difference to my total HP is too much

I notice it with sejuani cos is the champ that im playing most (i dont usually play tanks) of the times and is not soft, but sometimes is hard to build nice armor or mr if i dont know how does the enemy team kill me.

I could provide more screenshots, or more data.