100% guests did it. They could say "sorry, I just accidentally pressed 4 stars", but it's more easy to point the finger to another guy - Airbnb.
Have you experience the same in your school? Nothing has changed ever since. Those "never guilty" grew up and now traveling the world and staying at Airbnb places. And never take responsibility for their words and actions. It's Airbnb, government, magic is responsible for their own actions. It's because of Them!
It's very hard to deal with people like that. As they do things behind your back. Try to message them Before they can give you a review. Say something like this "if you feel we deserve less than 5 stars, please communicate with me". And during the guest's stay send message "I hope you are enjoying your stay. If any problem, please message me". This is not a 100% solution, but might help.
Write a meaningful and honest reply to their reviews. Nothing can beat a good, reasonable reply from the host, who takes care.
4 stars on cleanliness is not bad score. Superhost status is not everything. Actually the more you host, the more it's difficult to maintain the Superhost status. Number of reviews and time are more beneficial than the Superhost status.
Don't loose your motivation because of just few dishonest guys or those who feel self-importance and point the finger at someone else. It's the one, who continues to walk, will get into destination.