I believe it’s a cheeky reference to humans intentionally cultivating hot peppers specifically because of their capsaicin-producing quality. :)
You see a long time ago, someone at a tomato. Could've been a slice in a cold sandwich. Could've been a fresh one, maybe with A little cheese and pepper. But chili just won't do. Neither would spaghetti.
Then, before we had such regulations as we do today, they deposited that tomato seed, post digestion, in the train lavatory toilet. Being back then as it was, the tomato seed and associated fertilizer was dropped from the train car to the track ballast below where it germinated.
It's the same process where researchers deposit tomatoes on new volcanic islands.
You know what they say: when you gotta go, you gotta go.
https://youtu.be/dutpBSKj8JY?t=196
It looks at a couple non-competing (iirc) theories