When I read something like this, I start to question the validity of the method.

Psychologist Sam Gosling analyzed the Facebook profiles of 236 college-aged people, who were also asked to fill out personality questionnaires… surveys that were designed to assess not only how study participants viewed themselves in reality, but also what their personalities would be like if they had all of their ideal traits.
The Psychology of Facebook Profiles | TIME

The better experiment here is to have half the participants maintain a normal Facebook profile. The other half would create a profile demonstrating their ideal self. Then compare those against the Big Five questionnaire looking at both. The list of personality traits in the article “openness, agreeableness, conscientiousness, extraversion and neuroticism” gives away the test used despite not explicitly named. Of course, I’m no fan of the Big Five.

Should the results match you can say Facebook reveals whatever the Big Five measures. However, I’d be uncomfortable saying any instrument measuring self-reported information accurately reflected anything about a person’s real personality.