They're both.
Tbh... religion is a part of culture IMO - I don't believe in any particular deity and see religion as a man made. I don't think there is any need to automatically become an apologist for any particular religion any more than there is to criticise all members of a religion for the actions of a section of people who follow a particular conservative interpretation of it.
This case is linked to religious beliefs, I don't think trying to deny that is helpful - historically there might well be a culture of abusing women, killing them etc.. that predates current religious beliefs - I don't know if there is or not. However the current conservative religious beliefs being followed by the majority of people in Pakistan* are very much to blame for perpetuating the situation. Its those conservative beliefs that lead to women being treated as property, as second class citizens - its those religious beliefs that endorse punishments such as stoning for adultery leading to people believing that carrying on with honour killings has some justifiable logic to it. Its also those religious beliefs present in the court system that allow the family member of a victim to forgive the perpetrators... leading to the farcical situation whereby a family can conduct an honour killing and then family members forgive anyone prosecuted for it - essentially honour killings are also largely unpunished by the court system thanks to religious doctrine enshrined within it.
*ref the pew data for Pakistan posted earlier - majority support for death for apostasy, majority support for death for adultery.... frequent cases of lynch mobs stoning people after allegations of blasphemy - tis a very conservative version practiced over there.