If there is a temporary and immidiate boost in the number of organic downloads, then it is most probably as a result of Black Hat. Generally, the reviews are the main influencer for us to decide if an app is good enough and the one we're looking for or not. But unfortunately, there are some companies that use fake reviews to inflate app rankings in App Stores. They create a lot of fake accounts to leave positive feedbacks to boost app's rankings in a short time. Whenever you see positive reviews escalate in a short period of time, you may suspect Black Hat to be behind it. These kinds of reviews are generally very short and don't exist for a long time.