As well as having three of the 20 round mags as are pictured and being reasonably certain I bought from CDNN; I also have a 50 round stick Uzi 9mm mag that I also bought from CDNN and it is, I am sure, a USA brand mag. I'm sure because it really sucks and one tends to remember not to buy such things again. Other than being a black colored, Uzi 9mm stick mag, it is different in virtually every way from the pictured mag and the three 20 round mags I have.
CNDD is, for many items, a seller of out-of-business, surplus, over-run, and the like items. USA may have been a intermediary surplus buyer that sold mags from various sources to CDNN. Or USA may have been a company that had mags made for them from different companies and branded to the USA name (e.g., the Kirkland brand sold by CostCo). For a couple years, when CMMG first started making Atchisson pattern .22 conversions for the AR pattern firearms, all of the CMMG .22 mags were made by Black Dog Machine (BDM). BDM also made the .22 conversion mags for Spikes Tactical, and those were dual branded, as were the .22 mags BDM made later for 2A Armament.
So, unless you can find a physically branded example of the same type as that pictured, or run across someone from the manufacturer, I don't know how one could independently determine the actual maker.
Best of luck.
MHO, YMMV, etc. Be well.