What are the challenges for recognising the handwritten characters? This 2014 article saying that a Chinese team of physicists have trained a quantum computer to recognise handwritten characters.

Why did they have to use a quantum computer to do that?

Is it just for fun and demonstration, or is it that recognising the handwritten characters is so difficult that standard (non-quantum) computers or algorithms cannot do that?

If standard computers can achieve the same thing, what are the benefits of using quantum computers to do that then over standard methods?
Handwritten digit recognition is a standard benchmark in Machine Learning in the form of the MNIST dataset. For example, scikit-learn, a python package for Machine Learning uses it as a tutorial example. 

The paper you cite uses this standard task as a proof of concept, to show that their system works.