Social media like Facebook are harshly criticized for the propagation of health misinformation. Yet, little research has provided in-depth analysis of real-world data to measure the extent to which Internet users engage with it. This article examines 6.5 million interactions generated by 500 posts on an emblematic case of online health misinformation: the Facebook page Santé + Mag, which generates five times more interactions than the combination of the five best-established French media outlets. Based on the literature on cultural evolution, we tested whether the presence of cognitive factors of attraction, that tap into evolved cognitive preferences, such as information related to sexuality, social relations, threat, disgust or negative emotions, could explain the success of Santé + Mag's posts. Drawing from media studies findings, we hypothesized that their popularity could be driven by Internet users' desire to interact with their friends and family by sharing phatic posts (i.e. statements with no practical information fulfilling a social function such as "hello" or "sister, I love you"). We found that phatic posts were the strongest predictor of interactions, followed by posts with a positive emotional valence. While 50% of the posts were related to social relations, only 28% consisted of health misinformation. Despite its cognitive appeal, health misinformation was a negative predictor of interactions. Sexual content negatively predicted interactions and other factors of attraction such as disgust, threat or negative emotions did not predict interactions. These results strengthen the idea that Facebook is first and foremost a social network used by people to foster their social relations, not to spread online mis-information. We encourage researchers working on misinformation to conduct finer-grained analysis of online content and to adopt interdisciplinary approach to study the phatic dimension of communication, together with positive content, to better understand the cultural evolution dynamics of social media.