The keyword distribution section shows you how the keywords that you track are distributed after the last update.
For example, if you click on 'Top 3', you will see only the keywords ranking in the first 3 places on your keywords list. If you click on 'Top 10', you will see all the keywords ranking on the first 10 places and so on.
Under the Keyword Distribution in the Overview section and your keywords list below, you see how your keywords are distributed on the current day. Therefore, if you choose date ranges like last day, last 7 days, last 14 days, last month, ,etc., you will see all the keywords and their distribution on the current day.
Click here to check out the article on reading keyword data.