Unlimited food-box supply granted by the Demons Hate This One Trick achievement, an Exorcist reference.
Pea soup becomes permanently and infinitely available from all of Carl's Food Boxes as the reward for the Demons Hate This One Trick! achievement, unlocked during The Ceasefire when he learned that demon-possessed shells cannot be teleported. The joke is an Exorcist reference, matching the achievement text's crack about Father Merrin.
Carl notes it is the first of two achievements in the same session to alter the team's food boxes — the other being Crab Chowder!, which adds a "chowder style" option to everything. He recognizes both as stupid jokes, but observes that this sort of thing usually is not a coincidence.
Permanent unlimited food-box item and a hint that the AI is building toward something.