I'm not sure. I'm assuming perhaps evangelical Christian teachings? But evangelical Christianity is very mainstream. The population of evangelical Christians doesn't produce any more or any fewer violent criminals than any other branch of mainstream Christianity as far as I know. Every "group" is going to have "good" and "bad" members. We can't paint evangelical Christians with one broad brush, just as we can't paint all Catholics or Methodists, or any other religious group as all bad or all good.
According to the Conditt family friends quoted in the article I posted upthread, RIOT is just another Bible camp, basically. They say there's nothing radical, extreme, or zealous about it. So perhaps if Conditt was radicalized into some type of extremist non-mainstream Christian sect, which is yet to be determined, he became that way through other means or on his own when he reached adulthood and moved out of his parents' house.
I wish I knew what they taught their children. Families say things but it does not make it true,