What was the difference in the measuring method? Because when I go to doctors, they usually first measure my eyesight with a machine, which should give an objective measure of my eyes' defects. But then they also take into account my subjective "feelings" by having me read distant letters with different lenses (starting from what the machine measured, but doing some slight variations). Maybe your doctor just used the machine to measure your eyesight?
A problem is that during the subjective measuring the optometrists reduce the strength until your vision get worse. But astigmatism does not affect the vision so much. Then they get, you have 20/20 vision with the correct glasses, and 20/20 vision with weaker glasses, so they give you weaker glasses, even though they cause some blurriness
