It actually touches on that in the article.

Even Merriam-Webster notes that both names colloquially refer to the Virginia opossum present in North America and that the word “opossum” can be pronounced with its first syllable voiced or silent. Both possums and opossums have a flexible diet and eat various plants and animal matter scavenged from their surroundings. Despite these similarities, however, possums and opossums are, in fact, different animals.