It's hard to say what facebook's intentions here without inside knowledge, but I wouldn't discount it. The founder of modern propaganda and advertising, Edward Bernays, performed many extremely subtle experiments that had dramatic shifts in how Americans behave to this day. (By the way, Bernays coined the phrase 'public relations' to replace 'propaganda' after it had been co-opted by the Nazis).

He got women to smoke by calling them 'freedom torches' and orchestrating high society women to light cigarettes in a demonstration for suffrage.

He facilitated the modern retail industry by shifting American behavior from a 'need-based' consumer to a 'want-based' consumer.

There are billions of dollars being spent to increase the effectiveness of advertising and I wouldn't be surprised if one of the world's biggest advertiser used subtle tactics to achieve this aim.