"Corn" in UK English has historically meant cultivable grains in general, not "maize" specifically as in North America.

Also, "pumpkin" is a standard English translation for the Latin and Greek terms that, if you want to be pedantic, were just "gourd". See e.g. The Pumpkinification of Claudius [0]

[0] https://en.wikipedia.org/wiki/Apocolocyntosis

I think it’s a mistranslation. OF. popon -> pompon -> pompion, meaning a large melon or (later) pumpkin. I guess it was translated as pumpkin rather than melon.

Corn just means grain. The shift to being equivalent to "maize" is later, and I think not universal in English-speaking dialects (and obviously only happened after the Columbian exchange).

It’s a mistranslation of melon I think.