But I'm not sure how a CPFP could be taken as suspicion of attempting to double spend.
Because you're not replacing a transaction/spending the same input/s. Instead, someone who owns an unconfirmed output from the parent transaction spends it in another transaction with a bigger miner fee covering both of them -- child and the parent.
I know, I get that. Perhaps it's just just the information they received from a faulty set-up system they are using that triggered a doublespent error. Or it's intentionally set up that way.
Why do you even play on suspicious casinos like this? And how did you find about them?
They are not available in bitcointalk forum, or any other forum I am using, and I never heard about them before.
They have a thread on Bitcointalk dating back to 2020.
(
https://bitcointalksearch.org/topic/--5293254) However, the thread hasn't seen any new posts since December 2020, which is also the last time the OP and their forum representative was online.