This thread has been fascinating and Cullen's death will likely always remain a mystery. That being said, I find it highly unlikely that his death was caused by a Sasquatch. I do think it's possible that seeing one, could cause a heart attack or huge surge of adrenalin that could lead to panic, injury and even death.
However, a direct attack would have resulted in visible injuries and none were noted by the coroner. I have no idea of how a Sasquatch would kill but it's reasonable to think there would be signs of severe blunt force trauma, as well as possible bite marks or signs of strangulation.
I have not read any of the David Paulides, Missing 411 books but are there any incidents listed, of bodies being found with these types of violent injuries, or something similar?