Well, I wouldn't rule out a original handle so fast, it will just have to be dated if you feel like it.
there was a artifact found in this area (central Indiana) in the late 1970's that was a small stone axe head with the complete handle and in good shape. and also I have seen several that were found in the last 50 years or so that have handles as well. and all those were original Indian made as well. one thing to keep in mind, the Indian population in some areas was active till the 1850's or even 60's in areas of the east not counting reservations and the like.
if it happened to be buried in some clay or silt when dropped, and it was in a low oxygen environment it would last for many hundreds or even thousands of years.... then uncovered by something either by erosion or animal in the last few years... you never know how stuff gets brought up..
And the method of putting the handle on was a popular way of doing that, finding a green branch of hickory, maple or willow... or whatever was native to the area. Possibly it was carved to shape then steamed or boiled to make it pliable, then bent around the axe, then wound with green or fresh cut rawhide, the rawhide, when dried would have been darn near impossible to tear or bust loose.
So in short, it could very well be a original Indian made handle on a very nice axe... I've seen one from this area in person that was....