It is correct, an aero foil in Ground effect has a decreased downwash and resulting from that the induced angle of attack decreases, with a reduction of induced drag.So, with the decreasing of downwash/induced AoA the angle of the stall is decreased effectively in Ground effect... My FI always tells me to think of a pillow put under the wing in Ground effect, that makes the "falling" (respective: landing) easier for the pilot (with sufficient runway available ;-) )