The domain was registered in 2016 and then the person who registered it put it up for sale. It doesn't mean development of the roobet casino started on the very day the domain was registered.
This is probably where some review site confuse the years the casino was launched as they just look at the date the domain was registered.
I see it the same way. It's relatively easy to find out when a site was registered, so you can naturally assume that the casino in question was also launched at that time.
However, I don't understand why review sites don't simply contact the producers and ask "when did you start? Much of the information needed for a "meaningful" evaluation of a site can unfortunately not be found on the internet and is publicly available.
Probably they just go with the public data available instead of contacting the casino itself before reviewing them because it will put their reviewing quality under question if they are in contact with the casino and doing along the side but the stats sites also can refer the multiple metrics instead of just choosing the very first.