Looks like it was used for many years. I have a catlinite socket that I use with my bowdrill and have made thousands of fires without that much wear. Super nice find!
The stone would have been used on the top of the bow drill to insulate the users hand from the turning fire drill. The bottom of the drill is wood on wood. The friction causes hot embers to form which are caught on the birds nest of tinder. This piece looks like it was used for a long time until it wore through the stone twice.