I didn't make that up.
These guys did.
Frankly, I think there's another reason, which is not to say opium doesn't figure into the calculations, but it's more of a side-show.
You'll note that the Karzai government hasn't agreed to any of this, so really what we're dealing with is a non-story presented as a fact.
I think it's sort of like when you're getting kicked out of your girlfriend's place but you leave a few things behind just so you have a semi-legitimate excuse to drop in any time.
So, if for instance those 9,800 stay behinds were ever to be threatened by Taliban terrorists or Chinese terrorists or Russian terrorists or Pakistani or Indian terrorists, the long arm of Uncle Sam's law would have an immediate justification to come down like a ton of bricks with the full weight of Yankee military muscle.
After all, we didn't piss away half a trillion dollars in that shit-hole just to hand the place over to the bad guys.