This page doesn't count animals killed by other (non-human) animals. Mother nature is also cruel. I don't think that humans are the biggest animal killers. A single humpback whale likely kills millions of krill every day. One could even argue that eating whale meat is ethical because it saves millions of lives.

Also it should be noted that most of these farm animals would never have been alive if humans did not breed them in the first place so we shouldn't see death as necessarily a bad thing. We give them life and then we take it away. Every creature dies eventually - So do we.

I think the focus of animal protection movements should be based more on the ethical treatment of animals. It's important to make sure that all animals have the opportunity of a decent life before they are slaughtered; especially have room to move around in an open area with access to natural light.