Inosuke did not undergo the same training procedure as the others. He found out about the Demon Slayer corps by accident. What actually happened was he came in contact with a Demon Slayer in a forest. Then, he picked up a fight with the said demon slayer, which led to him being victorious, and he also stole the slayer's swords. He had a curious mindset about dealing with demons that could provide the challenge he longed for.