I found the part of the book which prompted the posts above, dealing with the comparison with Treponema. It is difficult to form a view as to whether this goes to the crux of the issues at the centre of the book, or whether it is simply an error committed for "artistic impression", but, at page 12, Newby writes of the time on November 5, 1981, when WB first observed the spirochete:
Through the microscope, he saw something else unusual: faintly stained spirochetes (threadlike bacteria) some slightly coiled and some in messy clumps. He recognized them as a Borrelia, the same bacterial genus as the African relapsing fever spirochetes he'd studied as a student in Switzerland.
If he has written, or stated publicly, that this was so the source needs to be located. The statement seems at variance with the facts as stated in the above 1982 paper that it was a treponema- like spirochete. This view was restated in
Steere, A. C., Grodzicki, R. L., Kornblatt, A. N., Craft, J. E., Barbour, A. G., Burgdorfer, W., … Malawista, S. E. (1983).
The Spirochetal Etiology of Lyme Disease. New England Journal of Medicine, 308(13), 733–740. doi:10.1056/nejm198303313081301
https://sci-hub.se/10.1056/NEJM198303313081301

If he knew that they were Borrelia, it seems that he was the only one who did, and he didn't tell his collaborators. The taxonomy only seems to have been established in 1984 with this paper
THE YALE JOURNAL OF BIOLOGY AND MEDICINE 57 (1984), 529-537 Taxonomy of the Lyme Disease Spirochetes
RUSSELL C. JOHNSON, Ph.D., FRED W. HYDE, B.S., AND CATHERINE M. RUMPEL, B.S.
Department of Microbiology, University of Minnesota Medical School, Minneapolis, Minnesota
Received January 23, 1984
europepmc.org/backend/ptpmcrender.fcgi?accid=PMC2590029&blobtype=pdf
It seems that there is currently ongoing debate about the classification of the Lyme Disease family of Borreliae. You probably know more of that than I do. It would however seem that mere visual comparison with the African relapsing fever varieties of Borrelia would have been unlikely to be conclusive.