When this song was released kindred was not released in public was in development / idea stages and back then Wolf and Lamb didnt have masks until later. And Amumu is already dead so thats why ingame kindreds taunt is :
Lamb: We Know Your Loneliness....
Wolf: But Stay Away!
Because Amumu is already dead so Kindred therefore cannot kill him so they are kind of scared of him.
Since Amumu is cursed for loneliness for his life its like in Kindreds actual lore, Wolf Chases Those Who Do Not WIllingly Go, Amumu does not have a choice since he is cursed and no one will be his friend so Wolf chases him and tries to find a perfect time to kill him but since he is dead there is no way to :D So instead Wolf leaves him alone :D
And in the video where Amumu explodes the mark of kindred is made showing that Amumu was being hunted by wolf and Wolf finds techniques to kill his Enemies slowly and painfully such as having no friends and taunting him about his Loneliness making him explode but after exploding he still didn't die and Wolf left him, And Amumu and Kindred would have known each other for a while since they were both born in Ancient RuneTerra.
An Extract From kindreds background:
"He pressed on, the frozen air burning his lungs. He looked once more for his hunter, but could see nothing but the darkening trees. The shadows closed tightly around him and he suddenly realized there was no escape. It was the black body of Wolf that was everywhere at once. The chase was at its end. Wolf buried his sharp teeth in the squire’s neck, tearing out ribbons of vibrant life."
Sounds a bit like what happened in the video?
well thats my conspiracy/rambling hopefully this helps you or post/edit some info to make it better thanks :D