They're not different words, as the origin is the same. They're the same word, with a slight semantic shift from one language to the other. And frankly, quince marmelade is not very different, in preparation or use, from other types of marmelade.

A similar case is the Italian "mostarda" vs the English "mustard"- two very different preparations, but both based on mustard seeds.

A real case of culinary false friends is the Spanish "aceite", which means (olive) oil and is derived from an Arabic word, and the Italian "aceto", which means vinegar and comes from Latin "acetum" (related to the English "acid").

It seems that the etymological origin of Marmelade is Marmelada