Newt Scamander walks off the ship and goes through customs, then walks through Manhattan, taking in the sights. As he walks near a bank, a niffler escapes from his case and runs into the bank. Newt follows and, in the process of retrieving the niffler, meets a Muggle named Jacob Kowalski. The two accidentally switch cases.
The date for this event is taken from the newspaper Newt notices when Tina takes him in to MACUSA headquarters. While the name of the paper, The New York Ghost, is mentioned in the script and therefore canon, the date may be simply the invention of the art department. That date does fit with the timeline of the story and the weather we observe, so we are using it.