If you try to use your browser's standard right-click Pinterest intercepts and gives you the option to Save (to Pinterest), open link (the very one you are viewing) in a new tab, see more ideas about education (on Pinterest!), see more from renee ma (on Pinterest!), or login or sign up for Pinterest.
If you click on the image, which is a link, it gives you a sign-in form.
Sure, the three dots are there to click; but "Download Image" is the only function listed. Why wouldn't it just be a download button...
Edit: And it's truly a 'download' versus viewing it directly in the browser...