Are the seventy thousand who will enter Paradise exclusively from among the Muslims?

The hadith (definition) you mentioned, found in the Two Sahihs, about the seventy thousand who enter Paradise without reckoning, does not mean that only they will enter Paradise. The Prophet, peace and blessings be upon him, saw a great multitude of his Ummah and mentioned that among them were seventy thousand who would enter Paradise without reckoning. These are those who do not seek ruqyah (definition) (incantation), nor practice tatayyur (superstitious omens), nor get cauterized, and upon their Lord they rely. The Ummah of Muhammad, peace and blessings be upon him, will constitute half or more of the inhabitants of Paradise.