Information theory vs system theory ( commented in Determining linearity, causality, memory, and time invariability from a picture of the signal)
Yes that's most probably a typo; it's the system theory which deals with the concept of linearity, causality, etc. 

Linear system theory deals with characterisations of systems in terms of its input-output relationship through applied signals. It describes how to compute the output in time and frequency domains as well as characterises systems according to their properties such as linearity, stability, causality etc.

Information theory deals with quantification of information (called as the entropy) contained within a source according to either its observed output (via statistical computation) or to its descriptive model (via probabiitistic computation).