Syrup? Never seen pineapple in heavy syrup

This recipe was a partnership between Food52 and Dole. If you look at the second photo in the recipe slideshow, you will see a can of the product clearly displayed.

For American cooks, Del Monte is another major brand that also produces a competitive product.

My guess is that pineapple in juice will work in a pinch. You'll probably want to drain it very well though to remove excess moisture.

Best of luck.