He advances each time she steps back. She didn't belong and he would drive the beast back into the sea for daring to try to steal from him. It was unfortunate she had tried to snatch his property and not one of Nico's. Though he knew Nico wouldn't just let her get away with it, he was far kinder. War had a mind to see this mare drown trying to get away from him.
He stops immediately when the large mare does and instinctively he moves back just before her forelimbs rise. Though he did not have much experience in actual battle he had been practicing. It was the sheer hatred filling his veins that could help him defeat an enemy. Her words keeps the snarl on his face. It wasn't really what she had said, but how she thought she could say anything at all.
The large mare does not turn into the sea like he wants. Instead she races down the coast like a cockroach that wouldn't die. He glances back to see Isla has retreated like a good girl. A smirk slides over his lips before he begins down the coastline to trail the draft mare. If she didn't leave the Inlet promptly he would force her to.