wpgraft reads the page as your browser rendered it, every element and the computed styles on each one, at every breakpoint you ask for, and rebuilds it as Gutenberg’s own native elements with the styles in Gutenberg’s own fields. It needs no access to your Wix account, no export file and no API key. If Chrome can draw the page, wpgraft can copy it.
Wix gives you no way to take your design with you, which is why "Wix to WordPress" usually means rebuilding from screenshots. wpgraft copies from the published Wix site and rebuilds each section as core WordPress blocks, with no page builder needed on the other side and nothing to un-install later.