Anyone have any ideas how they might have technically 'extrapolated estimates' of intelligence? Would they have used a language-based metric like 'idea density'

Anyone have any ideas how they might have technically 'extrapolated estimates' of intelligence? Would they have used a language-based metric like 'idea density'? Or is there another aspect to this? Would love to hear from someone with psychometric and/or data sci experience. It's very dystopian but I am curious how something like this is even possible