I'm beginning to suspect that it's a Wikipedia factoid...
Could be, it was too good to be true. Maybe even very likely it's incorrect.
I checked it's sources and they are
1- an italian multiplayer forum (for a game?)
2- a website that doesn't work about miniatures.
This is a more reliable source:
http://forum.axishistory.com/viewtopic.php?t=23884
If I understand it correctly,
maybe 10 000 were built and the large numbers only means the size of the order (which not necessarily are all delivered or even produced).
Furthermore using it succesfully requires enormous cojones; range 300 to 500 meters.
there's a nice picture of a Fliegerfaust lying on the rubble on the first page of that link to axishistory.
edit:
Back on topic;
if large amounts of this stuff is lying around from the '50s onwards, I'd expect more of them in the hands of the NVA/VC too, making helicopter landings in the jungle quite dangerous. Even the Fliegerfaust (or is it the Luftfaust?) had a minimum range of 300 meters, which would mean you'd need giant landingzones secured.