George DID know Marty was responsible for bringing them together. The box of books he authored showed Marty in his “alien” outfit. There are closeups in a YouTube video about this. Marty called him Dad at least twice in the 50’s. He also said not to go hard on a son when he started a fire. He’s into sci fi so probably figured it out. The theory on the truck is that George figured out it’s when the old Marty would be back, so it was a thank you.