Old AMD cards can be flashed with any BIOS that says anything. Maybe the card was used for a scam and flashed to say it’s an RTX 2070, it should have a switch to go to its 2nd BIOS near the top left (when slotted in). And if it doesn’t, you can just get its original BIOS off of Techpowerup’s database and flash it with atiflash, also from Techpowerup.
Picture stolen from some Reddit help thread for a red dragon RX 580.
This is assuming that Linux is reading what the card claims it is correctly. Which seems likely, since reading device IDs is a really important feature that probably works nearly perfectly.