(I hadn’t explored this aspect thoroughly and from my tests, following your message, here’s what it comes up)
When you import an existing HTML template, the images that are not used in the static part of your HTML are automatically imported into the WordPress library so you can select them to build your theme from the Pinegrow plugin.
So if none of the images in your imported project are part of the HTML, then you won’t find the folder in the root but the images will be available in the WordPress media library instead.
If the images inside your images folder are part of the HTML (used in the code), then you will find them available in your images folder which will be imported normally.