It's rude to complain about something that cannot be immediately corrected, particularly if it's in the category of "gifts". (And I'd hate to think the colleagues were viewing a drug rep's offerings as some sort of payment rather than a gift.) So, the colleagues were out of line.
However, if they had been told there would be a full breakfast, and hadn't eaten their regular breakfast, I can understand being irked at the misinformation (even if they shouldn't have made that obvious). My boss did that to me once - he asked me to come and do morning registration at a conference, and specifically told me not to eat beforehand, because the catered breakfast would be SOOO good. Well, I guess it was - because by the time I'd finished all my work, every scrap of it was gone. I was a hungry pup until lunchtime.