It should be "kelvin" here. ;)
Unit names are always lower-case[1] (watt, joule, newton, pascal, hertz), except at the start of a sentence. When referring to the scientists the names are capitalized of course, and the unit symbols are also capitalized (W, J, N, Pa, Hz).
[1] SI Brochure, Section 5.3 "Unit Names" https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-...
I think the author had it just right. There's a lot of inertia, but the traditional way can cause confusion.