IMHO, I think that maybe LowePro is getting ready to discontinue/upgrade the bag, and they off-loaded a chunk of inventory. Or, they just have too many on hand, and off-loaded for that reason. Could also have been purchased through an unclaimed freight auction, or similar.
I completely understand the Buy USA mentality, but you could never buy this from any US retailer at this price, even if they paid $1 per bag. They'd mark it up to a discounted 50% off, and sell it at $100. You have to remember - cost of living in China is a bit less then COL in the USA, therefore what I consider a survivable mark-up with differ greatly from a China based retailer/reseller.
Yes, there is a chance that this is a fake (and I don't think it is yet), but, even if it is, it's still a nice sized backpack for <$50. To me, just about any decent sized backpack is worth $45. Even a US seller would probably sell a knockoff for $75-$125.
Just my 2 cents (and I have plenty with all the $$$ I saved buying this bag from China).