I honestly don’t know how reviews work. That is platform stuff and an utter mystery.
But I think one thing that complicates it is that I think you can ask CoG to unlock the game on other platforms as long as you have proof you have bought it on one. Which doesn’t register as a sale but would open up for reviews. So some of those reviews might be people who bought it back as an independent game, but then once the Omnibus launched asked CoG to unlock the game for them there as well.
Also, I know that on some platforms, your reviews and ratings are tied to your region, so everyone might not see the same numbers. Which is annoying.