marsh,
I just tried an experiment to see how far off the iron sights would have to be in order to shift the POI 4.5 feet at 100 yds. The front or the rear sight would have to shift roughly 3/8 inch, or any combination of front/rear shift that equals 3/8". That is a lot. You shouldn't be able to even adjust the rear sight this much to one side or the other. If the barrel was bent that much you would definitely notice it. I think we can rule out the shooter causing this, no one can have that much flerk (flinch/jerk).
Two questions come to mind, 1) Are you absolutely sure it was sighted in when you put it away? 2) You do mean 4 to 5 feet right? Not inches?