Organic download estimation keyword results are calculated based on your current ranking for the keyword and the search score of it. Basically, if your app ranks in a high order for a popular keyword, there's a high potential that you'll drive organic downloads from that keyword. The calculations are updated daily, so if there's a sudden increase in your ranking for a highly searched keyword, the percentage for that keyword will increase.
The main idea of the tool is giving you a clue about the potential keywords that might get downloads. The accuracy depends on different factors. If your app is ranking for a competitor brand name, that is also considered as a potential keyword to drive downloads. If we have all of the relevant keywords for an app on our keyword database, then we'll be able to show you very accurate results. But let's say we don't have a very relevant keyword to your app in our database which is a significant potential to drive downloads; in that case, we won't be able to show that keywords in the results. So, in order to get the best results, you should add all the relevant keywords to your app in our keyword tracking page. Then, we will be able to provide almost 100% accurate results.