I think this can depend on how Japanese people view trans people. The way japanese media portrays trans women is that we are "men who like girlish things" or "crossdressers" They're gonna call themself an "Ojisan" because culturally that's what's expected for him to say and to be written. Just because he calls himself a man, doesn't mean he is one. I'm a woman, a trans woman to be exact. I identify as a woman, and I always have been. But I used to call myself a boy/man, not because I am one. But because I didn't know I didn't have to. The same could be true for him. He could be calling himself a man, because he thinks that's his only option.
Knowledge on trans people is very limited in Japan. I've watched tons of videos of interviews with trans people in Japan. One woman, had all her surgeries, and HRT but referred to herself as a gay man. When the interviewer asked her if she's trans the woman was confused. -- She didn't even know that was a thing.