They're feared by most animals because most animals (humans included) aren't willing to risk a fight unless they need to, while geese have a solid intimidation game, and make to believe that they're big and strong and will fight you.

A 5 kg dog can also scare off plenty of people. That doesn't mean an average grown person can't punt it across the yard if push comes to shove. Plenty of videos out there show what happens when one of these animals actually goes after someone's kid... the kid usually ends up fine to put it that way.