Maybe he likes Little Plum.

Leonardo is a famous Hollywood movie star. He looks very handsome and elegant. He is a movie star that many boys like. After Leonardo became famous, he had fans all over the world. Because Leonardo’s English name is translated into Chinese and there is another name called Leonardo. The name Leonardo DiCaprio was originally created by Chinese fans for Leonardo.

It may also be because your husband likes to eat plums, so you named him Plum. If you really want to know the answer, you might as well ask him in person. If there is any special meaning, I believe he will be happy to share it with you. After all, you are his closest person.