The answer is: its vocabulary and grammar.
The passage about Edgar Allan Poe contains formal writing characteristics, which are used to communicate in a business or academic environment, or with people we are not acquainted with. For example, the text does not include contractions or slang, it is not written in the first person and it makes use of the passive voice. Furthermore, it possesses some compound sentences, and its vocabulary consists of longer words than in informal language, some of which have Latin and Greek origins.