Think they could have had more fun experimenting with image indexing. Say you Google a nice location, for example: Edinburgh, Scotland. On that SERP there is two locations for images, the 5th and the knowledge box to the right has a map and image.
The first image in the 5th position image area is Wikipedia (hard to beat that), but the last three are local blogs and Flickr (easier to beat). The very last image is the same image used in the knowledge box which sits nicely in eye line with the 1st position SERP link.
After a quick bit of detective work I've found that in Google Images, Pinterest link back to their page but are not the image source.
Type into Images search: site:pinterest.com intitle:Edinburgh, Scotland
Back to the Edinburgh, Scotland SERP and looking at those images in the 5th position we can see that all images are both the page and source.
We can use the Flickr image that's third in the 5th position image area as grounds to warrant even a small experiment to test if the theory is correct. The theory being that if Pinterest was the page and source could they see a benefit from it reflected in their organic search traffic.
What Pinterest lack is content, which they stated in the post. What they don't lack is images and titles.