Over in Asia AMD seems to be rebadging Radeon RX 570 as 580 cards. It is a little unclear as to who, what and why but this isn't the first time something similar is happening. Basically, it's a new SKU injected into the existing lineup.

At the Chinese AMD website product pages have gone up, listing RX 580 having 2048 shader processors (Radeon RX 580 2048SP). And with an RX 580 that should be 2304 (which is the shader count for the RX 570).  The product could be an OEM inclusion for system integrators though. If you focus on the specs, AMD seems to compensate a little bit with a high boost frequency listed at 1284 MHz vs 1244 MHz. 

I very much dislike these confusing 'new' SKUs. If you live in Asia, be do be aware.