steam has a review filter, you can see the number of reviews on who got the game through keys. All the reviews are given keys, the person paid $100 to get the game on steam, then paid people to review his game though fake review websites. Then removed the game in itch.io for reasons we don't know, maybe to hide the fact that it maybe malware. Steam/Valve does not chech games for malware that is only through a computer, the person who made Cave Crawler has the traits of a scammer.
Viewing post in So how did Cave Crawler get so popular?
It's certainly an interesting theory but reviews are in two categories: "Steam purchasers" and "other" and a lot of completely free games seem to have all their reviews, positive and negative in "other". I'm not sure downloading a free game from Steam counts as a purchase unless you actually pay for something?