IMO, if this recovered body is in fact NH, it's possible the small mark on his head happened after he walked away on foot. The area where the body was found is described as swampy and difficult to reach by a vehicle. He could have easily lost his footing and hit his head. It could have been a superficial injury. At this time, I don't think a head injury resulted in his death. It appears his body washed ashore.
Body found near search zone for missing man in Dayton area
Body found near search zone for missing man in Dayton area