Since we all know that Roobet.com regularly hosts an Art Contest here on Bitcointalk and they say:
Bonus Free Spins!: Some lucky participants will be credited with Free Spins
I'm not sure if this is my fourth time joining the Roobet Art Contest on Bitcointalk. I've won twice but never received a free spin as a prize. I want to know if other contestants in the Art Contest have received free spins, even if they didn't win.
I have never participated in this contest because I don't have those skills so I don't know for sure about the free spins that participants get, but from the statement you included and I also checked directly in the art contest thread, it clearly states that only some lucky participants, meaning not all the winners or not all participants took part this contest will get a free spin bonus, and it is not stated the criteria for getting it so the award is random whoever gets it, only Roobet knows, and I'm pretty sure the lucky ones will have gotten it.
Getting free spins is really fun so we can try Roobet casino and if we are lucky we will get attractive prizes of course.