Honestly, it's pretty obvious this is a part of a promotion as well same with sportsbet but that doesn't necessarily make the approach wrong nor prove that the winnings were staged.
If someone won this big, then it's a milestone for the casino and imo, it's just standard marketing to post about it. My guess though is, the recent million winnings sportsbet gave them a push in a way -- perhaps made them remember the thing or smth which explains why the dates for their winnings thread were close to each other. OP did mention this was 8 months ago:
Why are we posting this 8 months after?
The 2023 just concluded, and when we recap the whole year, we realized there is this exciting moment that we feel we want to share with you all. In fact, we have had his permission a while back but was too busy dealing with other priorities until the end of the year when we realized there is still this gem buried in our drive.