Which image is the export function based on?

Hi! I want to use Figma to compose detailed previews of websites and then export the assets to load them into a CMS once the client has approved the look of a page.

I am planning on exporting these assets @2x, but I wonder which version of the image the @2x feature is based on.

For example if I upload an image into Figma that is 1500x1000 px at 72dpi resolution, and I place it in a container that is half this size - will the @2x blow up the small image, or will it use the original image I uploaded?

I did a quick test and I can’t really tell - here’s the file: