Smoking of anything, whether it's tobacco or cannabis, can stimulate the gastro-colic reflex, which'll make you need to empty your bowels. It's probably because of the early vaso-constrictive effect that happens when you smoke anything. Happens to a lot of people, and it doesn't indicate digestive problems necessarily.

Other things that can stimulate the reflex are eating. That is, when you add new contents at the top of the digestive system, it stimulates the reflex at the end. And also coffee and other hot liquids.