Look at what your endocannabinoid system is used for. Sleep, appetite, etc. When you smoke, that's a good deal of the reason why you get hungry. Normally, when you eat, it's because you are hungry, and your endogenous systems are requesting food. When you've had your fill, this system stops making you hungry by removing the pleasure from eating; taking away the endocannabinoid.
So if you simulate this hunger, with an exocannabinoid, and then go ahead and eat, you'll get the same result, your body will try to go to baseline because it knows it is full.
It's not blood sugar, or stomach contents, or amount eaten, it's simply your body, acting like all animal bodies do, and stopping you from eating yourself to death.