2) On political opinions, HBD is about an objective, falsifiable, scientifically mesureable characteristic of the world, whereas the other opinions are opinions.

That's not how I interpreted the item. This was a political quiz, so to my mind it's not about "Does X exist?", but "Do you favor more X than the status quo?" For example, liberal abortion laws exist, and feminism exists, and higher taxes exist. Similarly, HBD may exist depending on its precise definition. But what's politically relevant is whether you favor more liberal abortion laws, more feminism, more tax increases, more HBD. So it's quite likely that a substantial fraction of quiz-takers interpreted being "pro-HBD" as being simply an NRXish way of saying "pro-racist-policies".