I had a tablet (Archos) that has the same serial.
On my Galaxy S4 the serial is more unique too
I think it's just a standard serial of Android or something (Maybe lazyness of the manufacturer) LOL
If the phone is 2nd hand, maybe it it has been flashed with a custom-ROM? Some custom-ROMs set the device ID with a fixed value so all people using the same ROM will have the same device ID.
This ID is the one you get on many low-cost devices. I call it the "Chinese ID". I suppose that manufacturers have to pay something to Google to have an unique Android ID.