As TFA explains and other posters have also mentioned, they did not violate any code of conduct. Only the organizers have violated the code of conduct.

A conference for the members of a medical association has the stated purpose of providing a venue for the exchange of information between the members. When the authors of an article published in the journal of the said medical association distribute free copies of that article to their colleagues who attend the conference, they do exactly the thing for which the conference is organized.

Only a shameless liar can claim that such an action is a "violation of the code of conduct".