Helmets are a minority thing in the UK as well, fwiw. (Although not nearly-zero as in that video.) After a lot of effort by the various London cycling campaigns, promo photos etc for cycling in London usually don't have helmets in, either. (or lycra, or... cycling shown as a-thing-you-do-in-normal-clothes, as it is in other places where lots of journeys are made by bike.)

That is a v cool video! I like seeing the number of bikes around in London at rush hour (especially now the sun's come out again) but it's nowhere near as many as that. Yet! :)