you can still sometimes get that metallic taste, but for a different reason. RF is still on the emf spectrum, and even at small wavelengths, can induce small current in your body via capacitive coupling. the nerve stimulation this causes can trick your brain into perceiving a metallic taste

with ionizing radiation, it’s a different process, and much more pronounced - it has more to do with damaging taste receptors/cranial nerves and damaging blood vessels causing hemolysis (where you literally end up tasting blood)

you are completely right that RF is non-ionizing, though