“Heap” is a genuine Indianism, which is to say it is typical of Indian English, a pidgin once widely spoken by many Indians and whites (and blacks) when they tried to communicate with each other. The OED’s first citation is from 1832 by Washington Irving “‘Look at these Delawares,’ say the Osages, ‘dey got short legs–no can run–must stand and fight a great heap.’” Coming from a white novelist this may not be the most authoritative citation. The next quotation is from 1848 “An Indian is always a ‘heap’ hungry or thirsty–loves a ‘heap’–is a ‘heap’ brave–in fact, ‘heap’ is tantamount to very much.” J. L. Dillard in All American English reports that in 1871 one Indian called a train “heap wagon, no hoss.” Sounds like something a Hollywood script writer would make up, I know. (The better known term for train, “Iron horse” is also a real Indianism, used by Red Cloud in 1866).
The fact a word or phrase was used by Indians is not proof that it was coined by Indians. Some usages may have originated as humorous coinages by whites that were later picked up by Indians. I suspect this is the case with “paleface” first recorded in writings by a white man 1822 but used by Indians not too long afterward.