Ammunition has been selling in bulk wherever people can find it. To reach 1.5 Billion rounds, that's just 1.5 Million people each buying a 1000-round case.
You're right, though - this certainly isn't business as usual. I'm more pleased with this than I am worried... this is the closest thing we have in the U.S. to a "no confidence" vote at the federal level.
I know folks that are buying ammo by the pallet load. That's about a quarter MILLION rounds of 5.56mm.
They're wealthy though. I could only afford a case for each caliber I own and a few cases of match grade for my long arm precision rifles.
China has over a billion people. India is close to one billion.