English speakers were trying to describe things they had seen and eaten to someone who had never seen or tasted it before by using terms that the listener could understand. They used other fruits from Europe in their descriptions as well. For example, Prickly Pear, Natal Plum, Tropical Apricot, Sea Grape, Desert Peach, and Strawberry Tree. Apples were just the most common fruit, so it was the fall back when there was nothing at all close to compare to in Europe. Other cultures do it too. Actually, I am told that the Chinese name for Sugar Apple is "Foreign Lychee."