Dust and stems in packaged oats
I'm not sure what you means by dust exactly but stems are definitely a sign of less sophisticated processing and quality control. You should rarely, if ever get a stem. As for dust its very hard to say as it could just be oat dust produced when oats rub together during transport. If one brand consistently has more dust in the bag than the other then it could be from processing, maybe they are allowing more byproducts into their final product in order to save costs, or perhaps the dust is there because a less sophisticated processing plant. If one brand travels more than the other the dust could be from more rubbing and shaking. 

If the dust is not oat dust then its a definite cause for concern, you don't want real dust in your oats! That would definitely be a sign of poor processing and I'd personally avoid that brand. 

Having oat dust and stems in oats doesn't mean the oats themselves are bad quality, that's more determined by the wheat varieties and how well it was grown. It does mean there's labor involved to search for stems and perhaps sieve out the dust, which is inconvenient.