frankly, a body fat percentage drop from 31 to 22 % with a stable weight and no loss of inches sounds highly unlikely to me. I am wondering how long you have been training and how far apart those measurements have been taken.
Measuring body fat is not an exact science. There are several methods that can be used but all of them have shortcomings. How well your are hydrated and the time of day can play a role. It is very important to create identical circumstances when measuring.
My best guess is that there has been an error when the body fat was assessed.