What’s “a net grain exporter”? Does it mean one who has never do

What’s “a net grain exporter”? Does it mean one who has never done any imports? (课文内容)
【正确答案】：“A net grain exporter" should be one who has done both imports and exports of the item, but finally exported more than imported within a period of time.
【题目解析】：“净粮食出口国”应该是既进口又出口粮食，但最终在一段时间内出口超过进口的人。