I'm not an expert either, I'm not going to call it a "bad assumption", (we're both just a couple of laydudes on the internet) but it would be an assumption based on the paper that COVID spread among the campers and counselors. From my reading, it looks like the paper is apparently demonstrating an attack rate at this camp, but it doesn't indicate an index case status, or secondary attack rates. It's just a report that says, there was this camp, and there are some cases.