I opened “Organize sites” and clicked “Flat”, and noticed there were a few sites shown that I am not subscribed to, such as “Autoblog” and “i get jokes”. I’ve now realised that these are the sites that appear in “Global Shared Stories”.
Even if I untick “Show Global Shared Stories” in the Preferences, the UI still makes a request to https://www.newsblur.com/social/river_stories?page=1&order=newest&global_feed=true&read_filter=unread - and it seems as though the sites/feeds in the response are somehow included in the sites shown in “Organize sites” (but only when “Flat” is selected).
Next to each of those sites it says “undefined opens”, whereas for the “real” feeds that I’m subscribed to, there’s a number (e.g. “483 opens”).