No, there is nothing antropophagic going on here. My trusty visual French-English bilingual dictionary is quite clear that le diplomate is the word for everyone's favorite delicious dessert, trifle. This fact appears not to have made it to the synapses of the magnificent neural network that lurks within the heart of Google-translate, which insists on rendering the sentence above as: "Nous avons mangé la bagatelle". But that's what you get when you settle for the soulless machine-translation approach to life.
Note, however, that le diplomate can also mean "the diplomat", so if you find yourself travelling among, say, the Fore tribe of New Guinea, you might want to provide sufficient context to avoid any possible ambiguity.