I think the video was taken earlier before the crowd arrived for the rally.  From the linked Newsweek article-  The helicopter with "Trump 2020" painted on its side in patriotic colors was spotted before gates were opened to let the crowd in at 4:30 p.m. local time, according to KPNX. Sanders spoke at the event more than two hours later.  Here's an inside picture of the crowd. Pretty small. https://d.newsweek.com/en/full/1571823/senator-bernie-sanders.webp?w=900&f=4d1c409f524a581cdad72aa050cca664