Earlier chapters said his father was his bad ads teacher and is dead. We don't know the school but his father was teacher. Did I miss something.
the translators or author mistakenly wrote the teacher as his father, but it later cleared up (if you read the translator notes) that the old man was a "teacher" not a father and that Noh was an orphan for as long as he remembered.
Also, Noh states, not that his teacher died, but that he was gone as disappeared gone i guess. I would have to reread some of the chapters but yea that what I remember
Just because they both have unruly white hair doesn't make them the same person. Noh's teacher had white bushy eyebrows (probably because he was very old) and missing some of his teeth. The Demon Church leader had black eyebrows and perfect set of teeth and seems to be younger, like not an old coot. His white hair as we learn is its natural color, while noh's teacher's hair is white presumably because he is very very old. So until we get more into, Noh is not a student of the demon church