Perils of a rationalized legal system. It started out as meaning only fire, but in the current Imperial legal code, arson is defined as The volitional creation of a fire, water, or other hazard, regardless of its nature, causing the destruction of property and/or danger or harm to sophont life.
Inasmuch as fire isn’t the only spreading hazard that someone can maliciously whip up, belike. And if you go around creating plague hazards…