Here's a study that found the same effect in people with type 1 diabetes:
Dietary Fat Acutely Increases Glucose Concentrations and Insulin Requirements in Patients With Type 1 Diabetes, Diabetes Care, April 2013
Joslin did a great video:
It was a crossover design, so each person had a chance to eat the high-fat meal and the low-fat meal. When they ate the high-fat meal they needed more insulin to cover the same amount of carbohydrate. The meals had identical carbohydrate and protein, but different fat content (60 grams vs. 10 grams).
"Pizza is widely recognized to cause marked late postprandial hyperglycemia."