After the app was displayed among the first 5 items in the search list, many more people downloaded it. It's an amazing feeling to see that you were able to do something to improve the search ranking of your application. In the long run this method helped to promote android app and get a decent amount of daily downloads.
Google changes its search algorithm from time to time. If you notice a sudden decrease in downloads, either there is an error in Google Play, or the algorithm was changed. Both happened before and both will happen in the future.