Not sure what you mean? The game was made in the Spinoff app, so it gives you the option to open the app, but if you want to play the itch version (which I assume most do), you can press the play button in the center of the screen to start the game. Not sure if that's the ad you saw or if something else happened?
I selected play and after the first bit of text it took me to an external website trying to sell stuff.
That's odd. The only part of the game that I see that does that is the Spinoff button at the beginning that takes you to it's page on the Amazon store. I'll run through the game again tomorrow to be sure something weird did not happen.
Just hit the play button in the center of the screen. It is indeed a game.