> Hence the idea that it is a kind of toxin (not a “poison” if I understand the terms correctly)

The way I understand it, poison is an umbrella term that includes toxins, venoms, and chemicals. Its definition is basically "is harmful to living beings", while the other three are specific types/sources of harmful.

Edit: Ended up looking it up, looks like I got poison and toxin backwards. Toxin is the umbrella term.