Interesting study, but I don't necessarily agree with it from my experience. I was always kind and empathetic to others. I shared my toys and I am a born in. I think a lot more plays into it than just religion like upbrininging, personality, and culture - which is affected by religion, but not wholly. My parents were always kind and helpful. My mom was a caregiver and I would help her with some of the day out excursions ( saw first had how people can be mean towards people who are "different,), so maybe that shaped me. I don't recall being mean to or being instructed to ignore kids at school. Sure, I wasn't allowed to hang out with them for the most part after school unless it was for a project, but in school I had several friends, even had "clubs" with a few in elementary. They were also religious from religious households and treated people kindly and me even as a JW. Maybe I don't relate to the story because I'm more of a humanist than most Christians too.......and my youngest son is the epitomy of kindness towards others and he's only known the JW way thus far.
Adding - however, I do know of many JWs and religious zealots who would fit this bill. I've seen unkind atheists as well (my BIL, for example).