From his name, the old man is likely meant to be Obata Yogorou, the (fictional) son of Obata Kagenori, the historical retainer of the Takeda clan who wrote the authoritative history of the Takeda's military campaigns. Yogorou is a character in the Yoshikawa Eiji novel series Musashi. In the novel, the Obata military school was a target of the brash young Sasaki Kojiro's challenges. Obata Yogorou uses a very similar style to Sasaki's Ganryu and correspondingly wields the nodachi Torisashizao (birdlime-covered pole) which is an almost exact match to Sasaki Kojiro's nodachi Monohoshizao (clothes-drying pole).
Not sure if he'll show up again. He's a very interesting cameo but there's really no place for him in the story.