I watched it again last night and it was even funnier second time around, especially the bit at the end where they had the winning cheque ready for him but it ended up being stuck away in the background.
Although you never know for sure I would imagine that the bloke was thick rather than an actor. There's always a slight lag between something being filmed live and then being transmitted on a TV and this does seem to confuse people into looking idiotic, you see it regularly at football matches when fans see themselves on the big screen. And considering his usual methods I'd guess that he'd taken £5000 off several people and for the show picked the one who was most suggestible/desperate/stupid.
The casino was hilariously fake, which of course only reinforced your expectation that he'd get it right but by being "just one away" he was consistent with his claim of using physics (a genuine technique but one that can only predict the rough area where the ball will land) and therefore maintained his reputation while giving us all a lesson that there are no certainties in gambling. Which was a clever ending after the original lottery trick set-up.
And yes, his artwork is great. I particularly like the sadness of his Woody Allen and the way he's captured the absurd posturing of Brad Pitt.