I don't get why anyone is questioning the resolution: it is obviously 1080p! They wouldn't use any other resolution but the standard to compare things.
Maybe 1080p medium setting... All GTA V benchmark were made with very high setting, we don't know how the game behave in high.
The RX 460 has 2.2 teraflops, the R9 270x 2.69 TFLOPS, the R7 370 2 teraflops. In some games, the R7 370 even outperformed the R9 270x. The 270/370 can manage 43 fps in GTA V very high, 2xmsaa.
And with the memory compression thing , this little gpu might be more capable than what most ppl think it will be.