There's a few things here that stick out to me I'd like to address.
JackBit.io seems to claim provable fairness, but after a further chat with the owner it seems otherwise.
Typically using an onsite source of random wouldn't be an issue with traditional Provably fair methodology.
However, since they're mainly based off Player vs player, this creates a unique case.
In theory they are able to know the outcome of a game a player creates, and join if it results in a win for them.

In order to be truly provably fair as a PvP casino, Jackbit needs to be using an external source of random which can't be manipulated by the house.
Ontop of this it needs to be transparent and verifiable on that external source to determine the outcome for any player.
Why don't you show the whole correspondence?
https://imgur.com/a/IsuGCaRYou wrote that this is only possible in theory, also we have no reason to do it, In the message below I wrote to you that we will use external source (Random.org API) or other RNG verifier.
Yes, so why should the players trust your word?
When they can trust math instead and verify themselves?
You're asking players to trust that you won't do that and join winning games, instead of like a typical provably fair casino which uses math to back it up.