Yes, trusting random new people to change the site's code is crazy.
And I really don't see why anyone would chose to rob a few users in a very obvious way when they have the option of stealing using the seeds in an invisible way, forever.
If the "anonymous dev"-story is true, there's an explanation for this possibly:
The new dev didnt have access to the server seeds. So he cant steal directly.
But by making some players lose more, the site has a higher profit. Gains more commission. Dev's cut is worth more coins.
He had access to code, the simplest thing ever is to allow to set server seed from player, or to somehow reveal it to the player with for example post command or special crafted cookie which even wont be logged into nginx\apache log.