Definitely faked. A normal reaction would be to yank the hand away the instant the blade touches it rather than blithely carry on sawing through the entire thumb. Not sure why it was done frankly, it's not convincing - you can see it coming a mile off, and as humour it leaves quite a bit to be desired :?
The fake thumb is obviously attached to the board - a real one would fly off due to blade rotation. I actually did cut part of my thumb off on a tablesaw a long time ago The docs sewed it back on and it's a bit crooked and won't bend much (loss of tendons) but at least I still have 10 digits...