the video footage is here. Amazingly it pans a small area and Sayoc is front and center. What an incredible coincidence! Thousands of people at the rally and they get him front and center with several homemade signs. The signs are a collage of memes just like his shirt.
https://www.hollywoodreporter.com/news/michael-moore-reveals-video-bomb-suspect-cesar-sayoc-at-trump-rally-1155772