Just curious, have you tried a more uncommon paragraph? Could it be the case that the model simply learned the poem due to it being in the training set?
However, I can't determine where this is originally from...
https://chat.openai.com/share/b17ecc0b-570c-4e20-9556-23bfa1...
Then run it through the GPT-4 API and compare the output to the original.