Yes, impedance matching term refers improving return loss, but this doesn't affect the resonant frequency (hopefully), resonance which is given by the dimensions of the patch antenna.
This step match improve the transition impedance from the feed line to the impedance of the hexagonal patch itself, when this is fed on one of its lateral sides.
Compared to a rectangular patch (which by design could have a near 50 ohms impedance on its side) the hexagonal patch has higher impedance (than 50 ohms) on its lateral sides, and may need a type of impedance matching to the feedline.
But if the hexagonal patch is fed from one of its corners, may don't need any impedance matching circuit if the patch dimensions are chosen properly.