Their statement is correct since 6 months is the maximum duration for an investigation for a questionable gambling account history since this involves contacting the game provider if your use 3rd party games and it will take a lot of time due to the volume of issue from different website. Just ask them for update regularly so that you will know when the investigation is over. Many issue like this resolved after a couple of months depending on the game provider response to your case.
6 months is also the standard duration even on other casino if your account is subjected for investigation that involves 3rd party games. Most of the time they will question you when you are winning too often on a certain game.
It wouldn't take 6 months for the 3rd party to conduct an investigation though. I'd already be looking at this as a scam if it happened to me. Seriously, these casinos are unafraid of their users because users have submitted KYC and they know the address of the user.
But if the owner also has publicly posted their address, they better expect visitors they hold the coins for months.
Nothing is known about this casino though. Even if they scam, it's gonna be fine. Thats what they think,