I think "culture fit" here is a replacement for: "He isn't young and single and probably has a family, therefore he won't want to work 70 hours a week and stay

I think "culture fit" here is a replacement for: "He isn't young and single and probably has a family, therefore he won't want to work 70 hours a week and stay in our awesome fully stocked with free soda and snacks office 24/7 and instead actually go home after normal work hours, and we can't have that."