Chaps I don't really get this. It doesn't say in the super cub manual that you can stick the brakes on and water ski. It doesn't say in the aero commander manual that you can shut both engines off and do aeros all the way down. It doesn't say in the 707 manual that you can roll it. But they all make for great videos don't they!
Aircraft like the citation are only certified for +-2 degrees because that covers most of what people want to do with them but this bloke has obviously thought about it and that's obvious for two reasons. 1, he didn't crash it on the way in and if you haven't put some thought into flaring onto a 30 degree upslope you'll duff it. And 2, he's done exactly what you should do taking off from a slope like that and gone blasting through V1, rotate, V2 and left it on the ground up to the tyre speed so that he doesn't have to rotate and risk clouting the tail. Climbing away isn't the issue, the terrain is disappearing below you.
If the pilot is reading, nice one, do it again mister. I'm planning a day trip to Lundy in the global..