You can take into account that the prefix non- usually means “not” by means of the phrase nonpoisonous, for a material which is nonpoisonous is “not” toxic. Being an interjection to negate what was explained just before or reveal it as sarcasm, it is attested by 1900, popularized 1989 by https://remingtonhnsxc.ourabilitywiki.com/9175760/the_definitive_guide_to_papiertaschen