Their books are perfect, and I hope this textbook gets adopted by thousands of colleges. Our RISC-V future is bright, now we need one on SoC bringup and getting your OS running on that SoC.
I re-took Computer Architecture recently, and we used their earlier book "Digital Design and Computer Architecture: ARM edition", and it was also excellent.
They mean between the authors. It's a common added expression when discussing two or more people whose names suggest a familial relationship but there isn't one.