That said, a lot of these threads like OP's are impossible to verify. Sure, he won and got paid, but it's very hard to verify if there was a connection between him and the casino. Let's say you run a company and ask your friend to play there for free until you win something, then share the details of that win on bitcointalk and some time later, when people forget about it, send the money back to you.
Free advertising

Your theory makes sense, but it seems like it's a stretch since this isn't a new site or a struggling site. They have been in this business for years and seem to still be doing well financially based on my research.
Correct, Bitcasino is already a popular brand and very trusted here in forum that makes this kind of trick useless since they will not gain anything because they are already trusted to the forum. They are giving away too a 20USDT worth of free spin without any requirements on regular basis to prove how generous they are when it comes to promotion.
This topic is really serves as publicity from Bitcasino since they show how trustworthy and reliable they are to solve the case but thinking that they plan this just to boost their reputation is already unreal because they have nothing to prove here while they are solving all the case against them even in the past.