Take that article with a huge grain of salt though, because the writer seems almost entirely clueless about the subject (which doesn't stop him from pontificating of course)... and more to the point, the general conclusion seems simply incorrect.
Japanese has a huge amount of variation in information density, depending on politeness, etc. Other languages can vary too, but not to the same degree in my experience.
Informal, colloquial, Japanese can be extremely dense because by default much is left unsaid (whereas in English there are many cases where one states the obvious explicitly -- "I agree" instead of "agree" etc). This is particularly true for written Japanese because of its ideographic content, which is extremely dense, but it's true of spoken Japanese too. Japanese is famous for having many homonyms, and one of the reasons it has so many is that words for many things are short, disambiguated by character in writing, or only by context in speaking.
However when one is being polite ... Japanese polite forms (and there's a big range of them) can be absurdly verbose.
So, which form do you consider when talking about the "information density" of a language? I dunno, but most people don't use highly polite forms in everyday speech, and much speech is pretty informal (among friends, family, etc).... and in Japanese, informal speech is generally very short and blunt, more so than English.
[Japanese can sound pretty "busy" because of the staccato nature of its pronunciation, but that doesn't necessarily mean there's actually more information there...]