As per the article:

"But what if my container is ‘microwave-safe’?

Though various plastics are marked as microwave-safe—and plenty of plastic lobbyists have defended them as perfectly safe—the term is somewhat misleading. It’s simply referring to plastic types that won’t crack or melt when heated, not their chemical makeup. Supposedly microwave-safe products can still contain bisphenols, phthalates, and plenty of other potentially harmful ingredients."