What does it mean when the doc says after a glucose challenge test: "your liver isn't making any sugar"?

Not sure either ! The glucose tolerance test (of which less physicians are doing nowadays except for screening of gestational diabetes) is a test that is primarily dedicated towards assessing the pancreatic function in terms of Insulin production and if beta cell dysfunction (the cells that produce Insulin in the pancreas) exists. The liver functioning state is not assessed though this special test however.