When Ghost was being kidnapped, Callum was at the Ghost's house learning from Uncle Yuan. On Ghost's request, he had been working for Grandfather Luo as one of the head chefs.
Callum wanted to cook something that Ghost liked to eat and Butler Douglas grudgingly told him to find Uncle Yuan.
Upon hearing that Ghost was in the hospital, Uncle Yuan wanted to cook himself but Callum insisted on cooking.
Callum was great with knives, but when it came to cooking time, he tended to either put too much salt or too much sugar into the dishes.
That or he just turned the heat up high and burned everything because then "it's safe to eat".
In the end, the only dish that Uncle Yuan approved was the sweet and sour pork. It was one of Ghost's favorite.
When Callum was lovingly packing it into a Tupperware that he had filled with hot rice earlier, Uncle Yuan glanced at his watch and said, "It's almost 5.30 p.m. If you leave now, you'd be able to make it for dinner."