I got that used sapphire rx 580 8gb that gpu-z shows as rx 580 2048SP, which idk what it means.. I want to know if I got a fake Chinese version of the card as it didn't cause any problems installing drivers
Since you had no issue installing the AMD driver then you should be good to go than. Another recent User also had a similar RX580 2048SP GPU card but was having issues installing AMD drivers unlike you had.
AMD created controversy when it marketed the Radeon RX 570 8GB as a Radeon RX 580 2048SP in China. If you haven't been following, the Radeon RX 580 2048SP is basically a Radeon RX 570 8GB in sheep's clothing. The only major difference is that the Chinese rebrand comes with a boost clock that's 40MHz higher. Sapphire was one of the first AMD graphics card manufacturers to release its custom model of the RX 580 2048SP, and now it appears XFX wants in on the fun.
EDIT: I agree that you didn't pay for a soup up RX570 GPU card but that is something you will need to discuss with your Retailer or Sapphire Support plus you should have researched that model before buying it.