There's plenty of scams out there that use a custom gbios. So when you run a program like Gpu-Z to read the specifics of the card, it comes back as a gtx 1080, as that's a programable listing. However, if you look at the rest of the stats and compare them, the bandwidth is different, Texture/pixel fillrate will be different etc
example : This is a gtx970 2Gb for sale, look at the GPU-Z report
https://www.ebay.co.uk/itm/GTX-970-2GB-DDR5-192Bit-Gaming-Graphics-Card-VGA-DVI-HDMI-For-NVIDIA-GeForce/282938985777?hash=item41e07a4d31:g:SpsAAOSweMVa4CC0&_trkparms=gclientid%3D%5Esbf%3D%2360000000000000000000000%5E&_trksid=p2489528.m4335.l8656
This is my 970
http://gpuz.techpowerup.com/18/06/14/k9w.png
the only thing the same is the top 4 lines, but ppl are gullible or ignorant and would only see the top 4 lines and believe what it says. Dude is trying to play you with a false bios. Soon as you try to upgrade, you'd need nvidia to discover your gpu automatically, and it'd come back as a gtx1050 driver set.
Its a scam.