Yes you are probably right but the thing is that if he have an interstitial ad on app start then he had more then 10mil views and maybe many thausend's clicks. So you can make lot of money from such a simple app.
It will not last forever but still profit can be made.
I can not devote much time (especially mental concentration) to my app.
However, I'm pretty sure when it will be ready, I will be able to make "few" changes to it and consequently published a dozen similar apps within another year at most.