ThingManager is indeed a bad name, but I think the article is blurring the explanation with poorly chosen example. The example is more about wrong design than wrong name, there are certainly legitimate cases when you want a class that deals with multiple things.

ThingManager is a bad metaphor for a class that follows single responsibility principle (http://en.wikipedia.org/wiki/Single_responsibility_principle). It encourages you to stuff too much into a class because managers do many things, and it's not always clear what exactly they do - almost anything can be thought of as some sort of "management". The real reason is mentioned two paragraphs from the end - the name is simply too ambiguous.