It depends on how the law is actually worded. A prohibition on lethal weapons is not a legalization of non-lethal weapons. FTFA:
"Then Bruce Burkett of the North Dakota Peace Officer’s Association was allowed by the state house committee to amend HB 1328 and limit the prohibition only to lethal weapons. “Less than lethal” weapons like rubber bullets, pepper spray, tear gas, sound cannons, and Tasers are therefore permitted on police drones." (emph mine)
While it's true that anything that is not prohibited is permitted, this bill does not somehow make non-lethal weapons "legal" where they weren't yesterday. Aside form the FAA having a few things to say on this topic (including "NO!"), unless the statute defines lethal weapon narrowly, any weapon which *can* kill, even if that is not the sole purpose or design, is still a "lethal" weapon. Usually, the definitions of those things go something like "can result in death," which would include anything which has ever caused, or could be reasonably considered to potentially cause death.
tl:dr, this story isn't about weapons on drones, it's about corrupt politicians watering down restrictive in laws for their friends at the expense of public safety.