He's talking about the "B-grades" made by formerly known people/sites like Air-Randy and SDS. People have been throwing the "B-grade" description around to classify the kicks that those guys put out there.
A better term to categorize/describe the shoes made by those people would be "unauthorized" pairs (rather than "B-grades", because Nike does actually authorize some "B-grades" to be made/sold through outlets). They are pairs that were supposed to be destroyed (due to imperfections or different/early production runs; this is where the term "B-grade" came from for these pairs)... or they are pairs that were made using the same materials (or scraps) "after hours" in the same factories. Thus, they are "unauthorized" because Nike never intended for them to be sold/created.
As for determining which pairs are "unauthorized" or not... it's pretty tough. There isn't necessarily a set way to do it. Unauthorized pairs have a higher chance of having more imperfections than normal release pairs... but that still isn't the only factor (as there are definitely some normal release pairs that have imperfections as well). Also, unauthorized pairs usually have earlier production dates than the majority of the normal release pairs (this comes from the fact that many of the unauthorized pairs come from early production runs that were meant to be scrapped).
Again, there isn't always a set way to do it for each release... but if the things I mentioned aren't adding up, the chances are definitely higher that you're dealing with an unauthorized pair.
