maybe they had a check to determine total value of all collected seeds and then triggered auto sweeps from a certain threshold to guarantee a minimum.

Not sure what the game theory optimal way of stealing is!

That would make sense.

But perhaps they just made a transaction directly from the app to a hardcoded address. Not making any additional network requests might decrease the chance of being flagged by automated systems in the Appstore review process. Then again you could just disguise these requests as ordinary block chain connections.

I'm probably over thinking this and it was just a quick and dumb money grab.

Game theory of cybercrime is way too interesting.