How can I get the smokey flavour in Hor Fun?
Another option is Smoked Paprika. As Jolene wisely cautions, those liquid smoke products are very strong. And even though it might be "natural" smoke flavor, it can lend a "synthetic" taste to delicate foods.

Smoked Paprika has a much more subtle smokiness. Of course, it will also add color and additional flavor of its own. It sounds to me like this would work well with the recipe you linked, but you might try adding it first to just a small amount of your dish and see if you like the taste.

In any case, Smoked Paprika is an inexpensive addition to your spice rack that can be used to enhance many foods with a bit of smokey flavor.