I see this as a marketing effort to create a human connection with their brand in the "physical" world. It surely created buzz on social media. Who knows, one day we may see an Amazon truck next to an ice cream truck at a beach selling sunscreen and portable cellphone chargers.
Amazon will do anything to maintain their leadership position and to not lose even a single customer to its competitor. There is a reason bigger than two day free shipping why customers are signing up for Prime membership in droves. Amazon.com has become synonymous to everything in store and stock outs don't happen in this magical place.