Just bought Galaxy Note 8 but When I got the phone for the first time and started it up, it showed the recovery mode and I selected reboot system. The phone had 0 battery.
I've seen lots of unboxings and the phone starts up normally.
Is there any explanation?
My guess - it's a refurbished device 


OEM's typically ship devices at about 40% charge or little more as that is the ideal charge level for storage (from the OEM to your hands it can take months ). After refurbishment, this was not done and the already low charge dropped to near zero
During refurbishment, previous owners data is wiped out (factory reset) and possibly in your case it was done through the recovery options and carelessly not booted back to normal


To confirm , try using Phone Info -Samsung which has an option to check whether your device is refurbished (I haven't owned any Samsung device for a while, so I don't know if it works on your model or not)