The two hour window between eating and a physical Yoga (Hatha, Ashtanga, Kundalini, etc.) practice is a general guideline. Severe twists, forward bends, and prone Asanas, such as Bow pose (Dhanurasana), can cause indigestion or worse. Some people will vomit, if there is too much food in their stomach, during a physical Yoga session.
If the Yoga class is in a heated room combined with too much food in the student’s stomach there is potential for digestive problems.
This not only applies to Asana practice, but also to Pranayama. For example: Kapalabhati Pranayama, which consists of active rapid forced exhales, and is followed by passive inhales, could cause an adverse reaction if too much food is in your stomach.
Digestion is an individual matter, and it sounds like you digest your food very quickly. Age of the individual, the amount of food consumed, and the type of food consumed; are all factors in the time required to completely digest a meal or snack.
You could always try a light meal or snack before a Yoga class to see how you feel. Some of my suggestions are small portions of milk, fruit, salad, yogurt, cereal, or steamed rice. If the portions are kept small or moderate, most students should not have digestive problems. You know your body better than anyone, so use your best judgment.