When someone calls USCIS, he has several options to choose:
-- case pending
-- case approved
-- case denied
--...
Depending on the situation, the person makes a choice.
In your situation, it's different. USCIS affirmed, because they already approved the case, they do not have jurisdiction on it any more and you have to wait the National Visa Center to contact you.
It is strange to me because it's the first time that I learn that USCIS forwards an I-730 approval to NSC for a beneficiary already in the US. Usually, this path is for beneficiary outside the US.