The guidelines didn't say reviews couldn't be bad. They just said that IF you had issues, they had to be related to the game itself. There's a big difference between a one-star review that says: "I wanted to like this game, but the game controls are extremely sluggish and the camera tends to jump to awkward angles at the worst possible moments. There are also many trial-and-error parts where a moment of bad luck sends you back to the last checkpoint 10 minutes ago." and a one-star review that says: "This game sucks." or "Bought on day 1, game crashed twice, got no apology from the creator, demanded a refund." or "No Linux version."
The first example says literally nothing about why a game is bad and just makes the reviewer look shallow, the second one might be irrelevant a day or two after the first release upon game getting patched and the third one is just the reviewer being pissed that his favorite OS isn't supported and downvotes the game purely for that.
"Politics" has a broad meaning here. "The game's creator said something bad to me one day, so I'm 1 starring his game on this site" isn't directly political, but "politics" in this game applies because the review is useless to anyone who doesn't share the reviewer's personal pet hates and is just looking for reviews to get a better picture of the game's strong and weak points.
Examples of "political" reviews is a review of some of the Ys games where this one guy made a review saying "These games were stolen by the publisher. Don't buy them." (XSeed paid the guy who made the fan translation of some of the games to put his translation in the official release, but didn't pay his hacker buddy because they had the developer's official translation kit and didn't need his unofficial extraction tools, so the hacker buddy cried thievery)
Another example of "political" reviews is a review of Towerfall saying "One of the player skins is loosely based on Anita Sarkeesian. If you play it you will turn into a SJW-zombie and fund the SJW-movement!!!" I'm exaggerating here, but you get the point. :P
A game review doesn't have to say stuff like "This game is crap. Like Hillary. Vote Trump." to be political.