Can't say why your inspector would say that unless he understood that it was going to be one 20A circuit, which the Code has an exception which allows a single pole or MWBC (two-pole) 20A without an electrode.
Even if you qualify to not install ground rods you still can.
Where I live concrete encased is required if you are building a new concrete foundation building that requires electrodes. The normal method is to stub a piece of rebar up in a wall and use a J30-db to make the connection in the wall and use an MP2 in the sheetrock and blank cover to make connection accessible.
Edit: Ground rods are one type of electrode that satisfies the grounding electrode requirement. I can only imagine there was a misunderstanding somewhere and that he meant ground rods aren't the only (or preferred) method and I would proceed with providing an electrode for the garage as required by NEC 250.32(A). It would be a whole lot easier to put in an extra exposed piece of rebar than to need it and not have it.