Social media like Twitter, Facebook and numerous other sitres, blogs etc are a part of our digitised world. They are another form of communication, just like conversations, word-of-mouth, letters, newspaper articlres, TV interviews and so forth.
Anyone in a position of responsibility or involved in a regulated corporate, sporting, or other group needs to excercise the same level of caution about what they say, to whom and about what. With the power of social media through immediate distribution to a mass audience on needs to be even more careful - as the Apple shop ex-employee who dissed his i-phone online discovered.
A referee should maintain the same level of caution on facebook and twitter regarding conversations & banter that they would maintain in clubhouse and training ground conversatrions.