Maybe just got off the back of a lorry - would have been easier to just cross the road, 'cos either route is taking a chance
It looks like they are on the underside of the bridge in the top of the photo, only after it had been repainted. They are not painting.
I dunno..……………………. To me, they still look like Mexicans trying to cross the border. Hey! Maybe they're painting graffiti as they cross!