Since the “light” and “severe” adjectives don’t have a medical basis, they are based on how the autistic person makes them feel and hasn’t got to do with what the autistic person is actually going through in that moment or during other parts of their life. Someone could struggle to take basic care of themselves at home and be going through intense anxiety in the moment which will cause a non-verbal shutdown later, but someone they are speaking to could be surprised they are autistic and claim it must be “light autism”. If they interacted with that same person during the shut down, it might be “mild” or “severe”.

Having said that, I can understand how that language could help to get certain ideas across to people who don’t understand autism.