Hello Chris, I have termed "circumstantial" for Matthew Greundner because, even though he has the right name, age, location and time period to be the father of John Jacob Grinder, there is very little information available of Craven County, North Carolina between 1710 and 1750 and no direct link has been established as yet, although there is a very high probability that he was the father of John Jacob Grinder.
The Grinders of Craven County, North Carolina emigrated through England from the Palatinate region of Germany. This is the southwestern part of Germany, bordered on the Rhine River and adjacent to Switzerland. The German and Swiss migration to North Carolina through England, occurred in 1710 and was largely due to religious persecution.
In the last 292 years there have been thousands of Grinders born and hundreds of branch lines that still carry the Grinder name throughout the United States, so I can assure you that there are many other descendants of Matthew/John Jacob Grinder who carry the surname of Grinder.