It comes from (intentionally?) misleading docs: https://github.com/microsoft/BitNet/issues/391

(only suggesting that it's intentional because it's been there so long)

That issue appears to be the one that's wrong. From the technical report

> We evaluated bitnet.cpp in terms of both inference speed and energy cost. Comprehensive tests were conducted on models with various parameter sizes, ranging from 125M to 100B. specific configurations for each model are detailed in the Appendix A.