It confirms what most of the gunblogosphere has long suspected. The military arms being used by the Mexican Cartels are being run out of central and south american armories stocked using the US Foreign Military Sales system.
Does this mean that the US is their biggest supplier? The US did not sell those guns to the cartels or even allow them to be sold to the cartels. The US sold them to places like government of Guatemala. The government of Guatemala didn’t sell them to the cartels either. Corrupt armory managers stole them and sold them out from under their government.
Keep in mind that if you buy into the logic that the US is their supplier, then US FFLs are far and away the biggest suppliers of the weapons used in US violent crime. After all FFLs are how all those guns got to the market before they were stolen or straw-purchased.