Google still documents the Aggregate Ratings Rich Snippet, and examples like the one you mentioned and others (IMDb example) prove that this snippet still gets displayed in Google Search.
In the case of the mentioned page’s use of Microdata and Schema.org: They provide a
WebSite item with an
aggregateRating property. So the
AggregateRating item is for the aggregate ratings of the website, not of the page or the blog post. But for whatever reason they only include this item in their blog. (Side note: they provide a
description property for
ẀebSite which is different for each page; which is not correct.)
The fact that Google Search shows the Rating Rich Snippet for all of the site’s blog posts is strange, because the second guideline doesn’t seem to be fulfilled:
Make sure the reviews and ratings you mark up are readily available to users from the marked-up page. It should be immediately obvious to users that the page has review or ratings content.
and because the site clearly marks up (i.e., following the first guideline) that the ratings are not for the blog post but for the whole site, so Google Search should have no reason to display that rating for each blog post (this gives the wrong impression that the blog posts would be rated).