Let me take a stab at this( I could be wrong though)
An average rewarded video ad that's fully played earns around $50-$200 CPM
We'll go with a very conservative earning per view of $50 per 1000 full views
This app probably has a million users(maybe more) and claims it has 100,000 DAILY USERS.
So we take 100,000 users watching 2 ads a day and it pays the app developer around $0.05 per view($50/1000 views)
100,000 users x $0.05 x 2 ad views per user= $10,000 revenue per day
So out of $10,000 revenue, they pay a daily winner $1000.
I could be wrong about the rates of CPM since I haven't used rewarded ads much. This is my guess