They’re different facets of the same constructive and creative discipline dealing with information flow: the mathematical study and literature, the technical knowledge and the actual designing and writing respectively.
Information is a sequence of conventional signs that convey ideas; big amounts of information and dedicated machinery can be also used to encode, transmit and reproduce sensorial objects such as images, video and audio.
So, information flow design is all about creating abstract worlds: playgrounds and tools for, and about, the abstract mind (or small mind as it is called in some traditions), which is the only one current computing machines can deal with fast enough for our needs.
Being essentially constructive (it is deeply connected with constructive mathematical foundations such as Type Theory) and creative, although in a very peculiar field, information flow design IS art.
As any art, it leverages a technical body of knowledge and literature but then the growth and expression possibilities are limitless. Futhermore, it can be (and usually is) a collective form of art, not just an individual one.
Of course it is often relied upon in pragmatic matters and businesses, which are heavily based on abstraction and communication; in those contexts it becomes more of a craft. Still, you might be suprised in discovering that collaborative creation of (abstract) beauty and widespread usefulness is the main driver and motivation for many people in this field; indeed, a vast body of creations is open to anyone to learn, use and even power businesses.
Travelling through, studying and practicing consciously information flow design can merge the creative freedom of writing with the mind-opening experience of learning new languages and exploring new cultures: it can change the way you think forever and for the better, freeing you from fixed forms and prejudices while you meet and create endlessly new ways of seeing things along the way.