Honestly I think that "monsters" is a very DIFFERENT prompt from"supernatural creatures". Monster implies an emotional characteristic -- monsters are horrific, terrifying, repulsive, or disturbing. Supernatural creatures are just that -- something magical or fantastic.

For instance, say someone wrote a story about a unicorn. That's a story about a supernatural creature, and fits the prompt "supernatural creatures" without a doubt! But if wouldn't fit the prompt "monsters" unless they'd written the unicorn in a very specific way.