No it is not a cheat. Those gems are obstacles and they have chosen not to clear them (yet).

@_TheSpaceBeing_ , I think @yobbaha is referring to number of gems the user has. Not the island itself. The other thing is, why are there missing obstacles for the pictured island. I can't clear it unless I purchase the island.

@jamie_d In that case it seems like it could possibly be a cheat or they earned gems for ages without spending. I’m not sure.

@yobbaha Here you can see how to report something: https://forums.socialpointgames.com/topic/80/how-to-report-game-problems-to-support
I would report it. The support can see if it is hacked or not.