(I'm not GP) My answer would be that it's the difference between "Why do mosquitos have differential attractions to humans" vs "Why do mosquitos like Subject 33 more than Subject 28." The untestable assumption is that what makes Subject 33 more attractive to mosquitos than Subject 28 is generally applicable to the population at large. I agree intuitively with GP that finding 1/64 to be highly attractive in one sample and 2/5 in another would be surprising if this were following some binomial distribution, but the methodology for determining attractiveness was different between those participants (live test vs exposing mosquitos to a nylon that had been worn by the participant).