Who is that old ? What boy is he talking about

I'm guessing the old man was the one who told nok to stay away from jaeshin bc he will bring him great harm, and is also the one who made a deal with jaeshin to increase his life span but with the cost of his son's life (and because of the deal, jaeshin altered the book of life and was punished by his dad and sent to rhe human realm in the form of a dog)
so now the old man came back to kill nok in revenge for his son
something like that if I remembered the plot correctly?