8 years ago when this phone was new it even had a different charger connected sound (don't know what phone and firmware changed to the softer sound of now) so it could have easily been part of the phone. I doubt it is a jailbreak tweak as it happens before the phone boots up. Android does this when the phone is off as it doesn't turn on the phone for you, so if this is a clone this could be an indicator. The note about original screws is somewhat strange.
Today you don't get that battery screen as phones boot up too quickly (although they could have removed it like they remove everything). It still exists if your battery is empty and you try to turn on the phone. It will show a battery until about 5% and then automatically turn on.
The warning card is a little odd (don't update over WiFi, don't update without getting a notification, reboot the phone every 7 days, don't charge overnight) but it has a nice warning about water-resistant vs water-proof and about not keeping it in the sun. Maybe this is an introduction for completely new smartphone users.
What is interesting is that MacBooks do this battery capacity display if they are sleeping with the screen open and you connect power. So it would seem possible that the old iPhones did this.