From Bulbapedia, the community-driven Pokémon encyclopedia.
The old woodsman is a character of the day who appeared in On Cloud Arcanine. Ash and his friends first met this old man by his home in a forest as he was chopping some wood. Since they were searching for a wild Arcanine, they decided to ask him about it. The woodsman tells them that the Arcanine doesn't normally go down the mountain, but recently, he kept on seeing it everyday. He tells them that it goes to get Pecha Berries from trees and that it goes to a small pond as well. After that, Ash and his friends asked if the man had seen a boy and his Flygon. He says yes, even mentioning that he told the boy the same information on the Arcanine.
Because of the information the woodsman had told them, Ash and his friends decided to go the forest and pond. Even though they utilized their Water-type Pokémon and Munchlax's Metronome, they failed in preventing the Arcanine from using its Extreme Speed to flee.