I observe something similar in other online casinos, especially where there is a free spin of the wheel of fortune, as soon as you started spinning, the server already knows what you got and even before the end of the spin, this conditional win is credited to your account, at first I thought it was all about a big ping, but it turned out that it was not so.
All calculations are done in a fraction of a second when you place your bet or start a spin. Everything else is just a visual representation for a better user experience. The same applies to online roulette games, or for example, crash or plinko games. There's nothing to worry about, that's how it should be. This does not mean that the games are being rigged.