Exactly what it says. Only that they aren't completely without underwear, they sneakily edited the videos to make it look like they were naked (with the little mosaic boxes you see) and they actually wore skin-colored underwear on the trains. You know, because this is kinda illegal.
Somewhat SFW. I guess.

...
in my mind they are ALL naked!

I love Improv Everywhere. I wish we had a similar thing here.

I'm always naked.
under my clothes.