Hopefully you can return it? I'm an old woman when it comes to barrel wear - and that barrel looks very used. I took two Flock's to the range yesterday - and both barrels still look like new (G42 and 43). SIG uses a much better (I think) PVD finish on their barrels now so you wouldn't see anything like yours. I'm guessing the same as others have said here - somebody swapped out the barrel...

Edited to add: ThrowinRock's barrel looks like it has a PVD finish on it. Your's looks like cheap Parkerizing at best - somebody stuck it to ya.