What exactly constitutes kill stealing?

[Manzcar]

I was in goblin camp killing mushrooms and captains in my favorite spot. Now there are a lot of spawns in this area so I don't claim to have the entire thing beacause there are a lot of monsters in the area.

But once someone on a racoon comes zipping through and pulls them all like 10 monsters as I am trying to pull one of the Mushrooms.

Well I pull the mushroom and kill it and this person yells out I didn't pull all the monsters so you could pick one off.

My reply was sorry didn't really mean to do that to you. I've been killing here for over a half of an hour until you came along and took the entire area over. Sorry that I took one.

They just left the area after that. Which is worse kill stealing or monster hogging.