The book "Octopus: The Ocean's Intelligent Invertebrate"[2] which I have here says this on the matter: "By the way, the plural of octopus isn't octopi, because the word is Greek -- octopus to be exact -- not Latin. The Greek plural would be octopodes, but we call them octopuses."
You're not being pedantic as it pertains to this word in the English language, you're just wrong.
1. https://en.wikipedia.org/wiki/Octopus#Etymology_and_pluraliz...
2. https://www.amazon.com/Octopus-Intelligent-Invertebrate-Rola...