The study I think you are referring to was not about whether the two humps pattern existed - that was the initial empirical observation (contrasting with other subjects such as mathematics). Instead the study was focused on a test that the authors had hoped would distinguish the two groups in advance, which was later found not to work. That in itself does not mean that the two groups don't exist.
edit: Although I agree that the fact that someone doesn't understand Python right away doesn't mean they won't be able to learn, and I don't think Eliezer meant to imply that - it's just an easy enough test to offer the possibility of a quick win.
Performance being bimodal doesn't mean that aptitude is bimodal, though. Different teaching styles may have different transfer functions, as it were.
Trivially, consider a teacher who only teaches at the level of the highest-aptitude students and allows no remedial or catch-up work for the lower-level ones, versus a teacher who only teaches at the level of the lowest-aptitude students and allows no enrichment for the gifted ones. We'd expect the former to produce bimodal levels of student performance given normally-distributed aptitudes (because almost ever...
P/S/A: There are single sentences which can create life-changing amounts of difference.