IIRC, there is a bit more complexity than that to the Pirahã understanding of numeracy. Relative quantity is something they’re just fine at understanding, (with words for single/less, plural/more and same) it’s abstraction of quantities to tokenized values where they struggle. Which, I suppose, also interestingly lines up with the study results; the initial training period resulted in nodes associated with quantity, but those nodes were separate/unrelated to numeracy systems that developed with additional training.