For the purpose of causal inference / intervention evaluation, you must ask if a Christian retreat would have had this effect on those participants. Perhaps Christians feel closer after a Christian event, but I find Christian events somewhat alienating because I'm not Christian. I don't find aspiring rationalist events alienating, in part because I'm an aspiring rationalist. It's fun to hang out with people who have common interests, and depending on who you are, that group is a different group... for me, it's rationalists. Part of the point of the camp is that it has a similar bonding effect that any coming together of people with a deep common interest or aspiration can have, and in this case, the common aspiration is rationality.

Plus, at the camp, I did internalize skills and attitudes that have helped me a lot over the past (I.e. I've improved much more over the past year than I have in previous years), for example, looking more vigilantly for fungibility between my time and money, looking more at the reasons I do things and finding more effect ways to pursue those reasons...

Those particular effects I wouldn't expect from a Christian camp, just as the particular effect of feeling close to Jesus is not an effect I'd expect from a rationality camp. I just happen to prefer the "rationality" effects, and these camps are for people with similar such preferences.

Seriously, it's fun :)