Who would be liable for this medical visit?

My brother owns a remodeling company and he and his crew were at a private home doing some remodeling. A tree had fallen on a fence and the owner asked one of the workers if he would get it off the fence after work. The guy did and got the worst case of poison oak. He had to go to the ER, his eye is swollen shut, it has affected his breathing and he has had to purchase numerous prescriptions. He has no insurance. So would the homeowner be responsible or workers comp?