Is this a backlight issue?

Hi All

Looking for someone to help give me some answers. I’ve just gotten into fixing phones, i’ve probably fixed around 10 IPhones so far and pretty comfortable with it. I received an iPhone 6 from a friend. It was dead black when you first looked at it. She said she plugged her fully working phone into the charger one night, when she woke up the next morning her phone was black.

She took it to a repair shop to check it wasn’t a battery issue. No one had opened the phone up before the repair shop so it can’t have been a case of not unplugging the battery while replacing a screen etc. Anyway, I transfer her logic board into a fully working iPhone 6, just to check it wasn’t anything else and was indeed the logicboard.

Now tonight while plugged in, I could vaguely tell that their was life in the phone. It’s got a very dull light in the background, very similar to some backlight issues on here. There’s a photo to illustrate this below.

If someone could confirm this is a backlight issue that would be great and also does anyway have any ideas on how this may have happened? It seems odd to me, however because i’ve opened the phone up I doubt Apple will fix it under warranty...?

Thanks

Blake