I can't say for sure exactly HOW it's calculated BUT What's hot is a tricky beast but hopefully this helps. It really depends on if you've written anything before and your fan base, which are usually synonymous. People that are just starting out,can get on what's hot easier than some with 500 fans. This is meant to make it easier for new people to break into the community. What's hot is also extremely dependent on read to vote ratios. 20% of your readers voted which is pretty huge so WP figures it must be hot. Lol Hopefully this helps.