Yeah, I had to check that twice as well. But as it turns out, Sapphire has released a Radeon RX 570 with 16GB GDDR5 graphics memory. The product seems to be based on the Nitro+ design.
So the 16 GB is certainly not needed for any kind of gaming, you could, of course, argue that in ultra HD some games could pass 8GB, but really this card is not fast enough. So why a 16GB version then? Well, mining is the answer here. As it turns out
ASIC miners using hat is called the Cuckoo Cycle algorithm benefits from such big memory values and can utilize between 5.5 and 11 Gigabytes of memory. A lunch/availability date has not been confirmed yet, neither is the price known.