Here is the recipe in case you want to try it:
1/3 cup sugar
1/3 cup vinegar
1/3 cup water
2-1/2 Tbsp ketchup
1/4 tsp salt
Bring to a boil and stir this mixture:
1 Tbsp plus 2 tsp cornstarch dissolved in 3 Tbsp cold water. Stir until thick and translucent. Add pineapple if desired.