[tjgq]

At the end of the video, he does mention that it works for any digit. A more honest way to present the argument would be to start with "let x be any decimal digit..." but I suspect most non-mathematicians wouldn't be able to follow that.

[timinman]

Serious mathematicians will feel his title was misleading or dishonest. Considering the proportion of mathematicians to the general public, the teacher is probably not targeting mathematicians - he's a mathematician targeting the mathematically curious. With that in mind, the title is perfect.

[moron4hire]

I don't agree. I think the real power of his videos is that, if he is demonstrating anything about mathematics, it's that mathematicians aren't all pedants who can't communicate with anyone outside of their field without accuracy.