Ah, but we can go even further beyond in pedantry. This distinction is only exclusive when we’re talking about a living thing. When talking about the substances themselves, one is a subcategory of the other. A venomous snake is not poisonous, but a venomous venom is a poisonous poison.
This is also true. Poisonous doesn’t specifically mean “dangerous when eaten” when talking about the substance. It is an insanely broad category. It basically just means the substance is harmful.