Screen burn suddenly appeared on refurb. Scam?

Hi I bought a refurbed iPhone X on ebay 2 weeks ago. Very good condition cosmetically. Battery 85%. No face ID or True Tone.

The display looked great. I didn’t use the phone for a few days and let it run flat. When I used the phone again it had really severe screen burn. I can ready the labels of the ghosted home screen apps.

How could the screen burn have happened to severely and so quickly? Did the seller somehow do a temporary fix when they sold?

Cheers

Tom

Thanks for the info that's really useful.

Here's a photo of the ghosting. I don't see how I could have missed that in the first 2 weeks!

One interesting thing is that the ghost image has a different home screen image to mine, so it must have occurred before I got it.

If there's no software remedy I'll have to return it I think.