It's not entirely clear from the article, but the data they're using appears to include all types of Federal Firearms Licensees. FFL01 is the license for a traditional gun store. However I hold an FFL03, which is a license to collect Curio & Relic firearms. These comprise guns over 50 years old and some special items on a federal list. With this license I can purchase C&R-eligible guns and have them shipped direct to my door, unlike the general public who must transfer Internet purchases through a FFL01 licensee. I am not, however, allowed to deal in guns, just to make an occasional sale when I decide I don't want a specific gun any more.
AMA about FFL03 if you're curious, I guess.