That paper seems to be for the obsolete Mir-BFT protocol. The library readme mentions that they have switched to a newer successor algorithm called Insanely Scalable SMR (ISS) but they have not changed the name of the library which can lead to confusion. I have found the right paper which is unfortunately not linked to:
https://dl.acm.org/doi/pdf/10.1145/3492321.3519579