Wouldn’t it be fructose?
Tomatoes contain both (as well as sucrose). Depending on the cultivar and stage of ripeness, the fructose:glucose ratio can vary between 1:1 and 1.5:1. In general, fructose levels decrease (marginally) and glucose levels increase as a tomato ripens.
I suspect that what the owner of Prince St meant is that concentrating the sauce by reducing the percentage of water increases the perceived sweetness (though possibly at the expense of the "tomatoe-y" flavor depending on how the the reduction is achieved,
e.g., many of the characterisitc volatile compounds will evaporate before the water boils (though with the right equipment one could capture them in a distillation column/tube and reincorporate them after the reduced sauce has cooled).