I had similar experience with two other mfg. Had a box of Sierra GK 165's that had a 150 in it. I just tossed it. A box of Speer 120 gr 257's was mis-labeled. It was full of their 100 gr bullets. They replaced it with 2 boxes of the correct bullet.
I'm guessing in the case of only one 'wrong' bullet, one got stuck on the belt somewhere and fell in the box when it was filled. But who really knows. Maybe someone on a friday just before beer-thirty wanting to mess with a customer. Who knows.
Pay it forward - Kids are the future.
Rifles are similar to boats and young women...there's no end to how much money you can pour into them without making them any more useful.