Since water is required to create an effective rapid explosion dry ice bomb, it is a chemical reaction.
7th grade Chemistry fail.
The law stated "dry ice bomb"... it did not mention whether it had to be one that used water or not. And I assure you that water is not required to make them. Water only causes them to explode sooner. If you truly think that water has to be use then fine, go fill a 2 liter pop bottle with some dry ice and then screw the lid back on... sit it in your house and eventually it will explode. It wont happen in a few minutes, it might take hours or even a day or two... but at some point when the bottle gets enough pressure it will burst and will make as much noise as if you made one with water you just wont have the luxury of knowing when it will happen.