Minecraft wiki entry for Poison, associated text: According to most medical and zoological terminology, "poison" specifically refers to a toxin that is delivered to an organism via contact or ingestion. As bees, cave spiders, and poison tipped arrows inject the player with toxins rather, they deliver venom, not poison.
Pufferfish are both venomous and poisonous in-game, while real-life pufferfish are poisonous but not venomous, and their spines are used only for intimidation purposes.