I would just ignore the dpi/ppi and build to the pixel dimensions listed in the dimensions section. My best guess is that they're making a distinction between min res (72dpi) and best res (300+ ppi). But their documentation overall seems to have an often-confusing mix of digital and print specs, as is further shown in your screenshot where they've made sure to also point out that your ebook cover should not contain separations, something that would only actually happen for print (decades ago).
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