The archeologists came to the conclusion because they couldn't find any signs on the human bones of them being nibbled on. Which we guess would mean tooth marks. They also could find no trace of fava beans and a nice bottle of Chianti. Not only that, but they discovered that the "Donner Camp" wasn't the "Donner Camp" at all, but another camp. Which means that if there was some eatin' going on, it wasn't the Donners who were doing the eatin'. Of course, because the analysis only dealt with them bones, they wouldn't be able to know if instead, the Donners were just feeling a bit peckish.
They did, however, eat pretty much everything else, including the dog.
This came as a great relief to descendants of the Donners who now don't have to worry about their name being tagged with cannabalism. Far be it for us to say anything as our relatives didn't do anything as notorious (they were too busy trying to avoid being raped by Cossacks), but we think it would be rather cool if we were known for that. We probably wouldn't have been teased as much at school, for instance ("don't take his hat, his grandparents eat people!") Actually, we don't think it'll make that much of a difference because as that famous cowboy movie said (no, not the gay one), "when the legend becomes fact, print the legend."