“Kaas” is Dutch for cheese. Kees (or sometimes Cees) sounds like “case” and is just a masculine name which is often hyphenated with Jan (John). The origin of “yankee” is somewhat uncertain, so maybe it was Jan Kaas, John the cheese eater.
I once encountered a professional singer (operatic type) who had the last name “Kaasschieter” which means “cheese shooter” . . . Oh boy, I don’t want to go any further there . . .
snort ... chuckle ... :)