From what I understand by what Rhavar is trying to explain (which I will turn into layman terms for people who are like me that have hard time understanding technical talk) the game "looks" like it is fair but they do have a secret way of knowing if you are gambling by checking the seed or not.
I think the better explanation is:
If you go through the verification process for each individual bet, then each bet is actually provably fair. But if you don't do that process for each individual bet, then it's impossible to verify the bet later. They also know which bets you are able to verify or not. So from their point of view, they know exactly which bets they need to behave with (0.00001% for nerds like me who verify) and which bets they have free-reign to undetectably cheat.
This doesn't prove they're
actually cheating, just they have the opportunity to do so without anyone having proof. Which more or less defeats the purpose of having a provably fair system in the first place. If I was a betting man, I'd however bet they are abusing this to cheat. Basically because of the stats BitwiseOperator gave -- and they talk about their nonce system:
The Provably Fair and NONCE system makes your game 100% manipulation free.
But it's 100.00% useless! It literally does nothing other than making it look like the industry-standard provably fair system (which requires a nonce) but it's not! This to me also seems pretty suspicious.
Personally I'd strongly caution people against playing here...
I would hope that after this (regardless if they were honest or not) they immediately switch to the industry-standard provably fair system (AKA copy exactly what just-dice.com does).