To my knowledge they're not related at all (and of course I'm aware that's not his dad, since the whole conflict of the manga is between Shiro and his father), but I didn't delete it because "dad" is a (rather archaic) term that has been used by young people talking to older people. For example, in an early episode of MASH, Hawkeye Pierce refers to General Barker as "dad" while they're doing a surgery together, and in the 1992 movie The Babe, John Goodman as Babe Ruth refers to every older male character as "dad".
So, I just chalked it up to the equivalent of a young person calling an old man "pop" affectionately today. I generally don't want to edit the MTL unless it's just so bizarre or unintelligible that it can't be understood because going through Paint and manually erasing everything and then trying to fit everything back in again is time consuming and difficult. Granted, I will do those edits when something mistranslates or doesn't translate intelligibly, but it doesn't seem to me like it's all that necessary in this case.
