As a player, it has been my experience that the top 10 civilizations that you have met will be displayed. If you have met more than 10 you can test this by selecting each of the categories in the list on the left and seeing if the civilizations that are displayed changes. I expect that the list will change since each civilization has its own strengths and weaknesses and would therefore appear in the top 10 in some categories, but not in others.
I checked it, the list is fixed and does not change by selecting other categories.
These are not the 10 top best civs, they seem to have been choosen at random.
