One on one, very laid back. I was interviewed by the camp director. There was little to no focus on why I wanted to work there, or my previous camp involvement. Rather, it was more of her trying to gauge who I was as a person: what I did in my free time, what I wanted to do in life, what I enjoyed studying in school, etc. Very easy. However, this was back in 2014, and the camp administration has changed since then, so things might be different.
Even though you have to "apply" to work at the camp every year, returning employees are not interviewed. This is something you only have to go through once.