"non-resident taxable person" is defined is one who occasionally undertakes transactions involving supply of goods or services or both, whether as principal or agent or in any other capacity, but who has no fixed place of business or residence in India.
NRTP is thus a special category of supplier in terms of s.2(77) with certain special provisions applying to it e.g. minimum threshold limit does not apply to NRTP and it cannot go under composition scheme either.
Non resident with fixed place of business in India will not be NRTP but if such establishment is making taxable supplies, it will be anyway covered under regular provisions of the Act; specific provisions w.r.t. NRTP will not apply to Non resident with fixed place of business however.