Quora is a website where users generate the content entirely. They post questions via threads and other users answer them. It’s basically a yahoo answers type social network that works like an internet forum. Both threads and answers can receive “upvotes” which signify the answer was worthy and popular. The answers with the most upvotes are put at the thread’s top.
It appears that the reason this page from a little-known website is able to rank amongst the bigger players is that the content itself is more focussed. It talks about how to name images for SEO, whereas most of the other pages are more general guides to image SEO—which all presumably mention the importance of naming images correctly, amongst other things.