Those who doubt the credibility about his big win story is high likely because the story came from newbie accounts but they do not see where the newbie account played.
It is normall if there is a doubt, even if the story come from high rank members, I'm sure there will be still some people who doubt about the story.
The most possible reason why people doubt about it is maybe because they think that the story is just from shill account.
In this case, bitcasino has proven that they are legit casino for years already and there is no way that they will risk their reputation for such amount.
I believe the story gives enough proof of his activity, so I did not hesitate to believe that the thread creator did win that amount. But I never doubt that Bitcasino will not pay the guy. It is given that whenever there is a huge win from freebies, the casino system will verify the wins and check for possible exploits. And if it comes clean, the guy is lucky that Bitcasino verified that there is no foul in the gameplay, so Bitcasino releases the winnings the moment all is cleared.