Hyun+Sun's+thoughts

In my opinion, this rumor is probably a propaganda. The animals who were capable of reading alphabets clearly saw that Boxer was carried away to get killed. However, Squealer and the pigs wants to hide the fact that he has been killed brutally. If the "truth" gets revealed, the other animals will start to see that the pigs were treating them unequally, and did not follow the commandments. And so, by covering the "truth" with a nice worded propaganda, the innocent animals are easily deceived and believe what Squealer says to them. The propaganda use was a big role since it always created a good-side about Stalin or Napoleon.