He was eventually there with some friends, as paparazzi caught him hugging his pal Thomas Houseago when he also showed up to help hand out groceries; Houseago reportedly stuck around even after the Once Upon A Time in Hollywood star left.
The only reason Brad Pitt was probably even caught in action was because at one point he took a break on the back of the truck and pulled off of his mask so that he could light a cigarette and smoke, confirming his identity.