How is non taxable supply different from supply treated as neither supply of goods nor supply of services?
There should be a supply first for an activity or transaction. If an activity or transaction falls outside the scope of supply then it cannot be said as a non taxable supply. I.e, although it called to be a Non taxable supply there should be a supply first.
You need to first determine whether a transaction is considered as supply under GST. Once it meets the criteria of supply, you will apply GST related rules. A non-taxable supply is a supply on which GST is not levied. It can be brought to taxation at a later date or the exemptions can be removed. A transaction that is not supply will not fall within the taxation purview.