See, those are tall ledges. I totally get how that's possible.
Pretty sure the variation in question is on a ledge that isn't as tall.
I had it happen again today haha.
seems you get some funky results if you can trick the game into starting one trick and connecting another.
If you can get the game to think you're attempting a wall ride and land in a grind it puts you down the wall without the need to disconnect manually. No timing really needed.

This holds true for legit Wallies too.
If you go to the Kube tower in skate 3 and find the shaded area that is a manny pad next to a wall.
Halfway between a wall ride and landing into a nose or tailslide there is a brand new animation to manipulate.