$2000 per month is with wealth right now. It will be more than affordable in the future since the country will have more wealth in the future. Pretty much everything in current economics relies on wealth growth (pension funds, 401ks, etc), so adding this into that mix is very reasonable.
the relationship between the two figures is that $2000/month is roughly the safe withdrawal rate for diverse $500k portfolio (ie, the most you can spend without risking that you use up the principal over several decades). if you use the almost all the returns from the nation's capital to pay out $2000/month, there isn't much growth to speak of. of course, it's sort of a naive analysis to treat a nation's wealth like a retirement account, but the idea clearly doesn't pass the "back of the napkin" test. there would have to be some powerful knock-on effects to make it halfway viable.
Growth where? If you "pay out" returns from the nation's wealth to its own citizens, the wealth still stays inside the nation and wealth growth still happens.
