Hello @Pg4
Airbnb have always used this system whereby guests are asked to evaluate us on 5 sub categories from a scale of 1 to 5 and then comes that all important question "Overall satisfaction" and this is the one that counts for the most and is NOT an average of the scores given for the sub categories I'm afraid.
Guests are told that 5* = exceptional stay and a 4* = very good
You can ask your guest for some feedback and explain to them that although Airbnb tell guests that 4* is very good, it's not in fact in Airbnb land and you no doubt received an email from Airbnb telling you to see what you could improve on but without feedback that's difficult to do.
Another solution that some hosts use is to "educate" guests on the review system by putting in their house guide an explanation on the Airbnb review system or by using a magnet that does this, that you can buy on Etsy for example
Below you'll find an earlier discussion that might help:
https://community.withairbnb.com/t5/Host-circle/Rating-system-in-house-manual/td-p/2288078