Apart from the hilarious joke, this quote makes the point that "will kill you" is not actually the same as impossible to eat, which more generally generally points out that impossible is often used in place of "really bad idea."

I read edible as a synonym for eatable. Poisonous mushrooms: edible. rocks, not edible. That's how that word is attatched in my head. I assume you read it as non-poisonous/fit to eat so it feels like a crass and overt redefinition. If the guy who wrote that reads that word the same way I assume you do it's a really cheap joke. If he doesn't the quote makes a lot of sense.