Question on View All Images link

When I click the 'View All Images" link I get a page with a list of all images. There is a caveat that says “Images are what are currently being served from the given url and may not necessarily match what was loaded at the time of the test.”

So my question is whether the images size on the page represent what would have been downloaded for the given device. For example, when I run a test for a mobile device I would expect that the images are smaller. This seems to be true for most sites but others it looks like a full size image is being downloaded.