His test is not a very good predictor: most of those who appear to use a model in the pre-course test pass the end-of-course exam but so do many of those who do

His test is not a very good predictor: most of those who appear to use a model in the pre-course test pass the end-of-course exam but so do many of those who do not. And it doesn’t predict the level of performance, as we discovered when we tried some deeper statistical analysis (Bornat et al., 2008). But the phenomenon is real and the prediction it makes is reproducible, as Dehnadi showed in a meta-analysis in his thesis (Dehnadi, 2009). That meta-analysis is summarised in (Dehnadi et al., 2009). But that’s not all. It’s not enough to summarise the scientific result, because I wrote and web-circulated “The camel has two humps” in 2006. That document was very misleading and, because web documents persist, it continues to mislead to this day. I need to make an explicit retraction of much of what it claimed. Dehnadi didn’t discover a programming aptitude test. He didn’t find a way of dividing programming sheep from non-programming goats. We hadn’t shown that nature trumps nurture. He had, however, found a predictive phenomenon, though he had no explanation of it. How do you read these paragraphs, or what part of the retraction supports the "two humps" claim and how do you understand that claim?