Well, this is a sociological question more than a historical one, but I can tell you that like most religious inhibitions the mormon opposition to alcohol is not as strict in practice as on paper. Especially in Mexico where alcohol drinking is a more prevalent social activity for whatever reason (anecdotally, some of my Mexican friends report drinking small beer even as pre-adolescents and having generally higher cultural exposure to alcohol than in the USA) people might set aside their doctrinal proscriptions in some situations for the sake of tradition and sociability.