iPhone bends at 70lb of pressure according the consumer reports, which isn't much at all. If you sat on it on a soft chair, it would be bent.
He's applying easily that force on a smaller area (thumbs) so I'm sure it would bend like that no problem.
For people saying it's fake and don't believe that result - make a video of you applying that pressure to your iPhone 6/6+ and see what happens.
I wouldn't do it to mine because I'm sure the phone is a bit flimsy. Don't care though, still loving it regardless. I'll just make sure to treat it gently.