Should he pay the vet bill or not.?

I have a friend who recently chased off a neighborhood cat from his garage because it was eating his own cat's food on several occasions. He chased it off with a broom and accidentally hit it. It turns out that it was the neighbors cat and they took it to the Vet ER. Turned out the cat was fine just had a small abrasion and now the neighbors are asking him to cover the vet bill. Should he have to pay the bill or not.