Grr... It wasn't even that. A couple of days ago, the hosting provider had some kind of server bork. I complained, and I guess as they were looking at it, they renamed the plugins directory (fairly common practice).
After they figured out it was their server, they never went back and renamed the directory.
Other websites have full lorem ipsum pages or have someones dubious web shop selling crystals running in a subfolder.
(Idea for webmasters: set up a few scheduled search for <words that should not be on your website> site:<yourwebsite.example>)