If your GPS had it at 3.10 miles, then it's not 5000m.
A full 5k course should be wheeled at 5005m taking all the tangents to get the shortest route possible. In a race, it's unlikely you get all the best tangents (you were probably in a pack for at least part of the race), and - assuming you were running or at least jogging and not slowly walking the course - GPS will always say the course is LONGER than it actually is (because the satellite tracking will bounce back and forth trying to keep track of you, rather than in a straight line).
3.10 miles is 4989 meters. GPS is probably going to be about 0.1-0.4% too long (depending on how many turns and how sharp the turns are, etc.). All that doesn't mean the course was DRASTICALLY short, just that it's very likely a bit short of 5k (maybe 20-30 meters short if you were hitting all the tangents perfectly, or maybe up to 50m short if not).
None of that really matters, though, because it's cross country. What can tell you something about how impressive it is is how times at Portage tend to compare to times at other courses. It's not a blazing fast course, but it's certainly not on the slow side either. Fisher's 14:43 is impressive, but it's not nearing Ritz's 14:10 just yet.