As others have noted, it is a "Dubai replica".
In Dubai, there is and always has been strong demand for gold to be in coin form, rather than as ingots or bullion rounds. As such, it is legal to manufacture and sell fake gold coins - provided the manufacturer uses actual gold to make the copies, and that they clearly mark the actual fineness of the gold on the replica coin. Government inspectors routinely check up on the gold dealers down in the famous gold souk, to ensure they are complying with the law and not selling fraudulent counterfeits. "21" would indeed be for 21 karat gold. The replica-maker is presumably hoping that the occasional unwary buyer will pay full 22k gold price for a 21k replica.
You occasionally see 22k replicas made and sold as well; here, the replicas will weigh slightly less than the genuine coins, so again, there is scope for the seller to skim off some profit from the careless or the uninitiated.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis