If there's no lightning bolt marking, it's just a charge & USB 2.0 cable, not thunderbolt. Genuine Apple Thunderbolt cables are marked, and the one you got with your MacBook for charging isn't one.

Does it have frayed rubber isolation around connectors and randomly along the cable? If yes, then it is a genuine Apple (tm) cable. If it has solid isolation ad looks good then it's probably a Chinese knockoff. :)

You either have a fake cable or a USB 2.0 charging cable