It actually was all about polling believe it or not (sound familiar?). That was the first election pollsters used telephones to poll people. Who had telephones at the time? Typically wealthier people and at the time wealthier people typically voted Republican. So they had a way bigger Republican sample and that’s why the polls showed a blowout victory for Dewey. The Chicago tribune owner was a big Republican and wanted to get out ahead of the inevitable so they printed those newspapers and put them out the night before so they could be first. Turns out sections in the paper were printer upside down, grammar issues all over, and Truman won. The Chicago tribune still has the patent/copy right of the paper.