A tough and interesting question. I had to look up the meaning of the word "Coterie"! Coterie: a small group of people with shared interests or tastes, especially one that is exclusive of other people. From this we can assume that he means that "communities of practice" is the oposite. A large group of people who are inclusive of each other. He thinks that studying the language use would help to define the question. Are there small groups of people who are linked by language, race and belief? Or does the University generally have larger groups of people - who are more inclusive of one another and speak the same language, have the same beliefs and so forth. Community is generally used to talk about people who are like minded: community /kəˈmjuːnɪti/ noun 1. a group of people living in the same place or having a particular characteristic in common. "Montreal's Italian community" synonyms: group, section, body, company, set, circle, clique, coterie, ring, band, faction; More informalgang, bunch

In this context, the distinction appears to be between one large, shared pool of language for the university - a single community - or several smaller pools of shared language, probably clustered around particular departments or disciplines - multiple communities definable by their shared usage of language particular to that subgroup.