I took a shovel out yesterday to check the hole (found out HF shipping is really slow, my pinpointer may be here Friday... almost 2 full weeks after I ordered it).
This appears to be my culprit...
It was about 8 inches down and 2 inches to one side of the hole. I still get a hit on the bottom of the hole when in pinpoint mode but I dug a section about 24 inches long by 8 inches wide, and 8 inches deep so I could swing my coil in the hole and it doesn't seem to pick up anything else in the hole in regular mode. I suspect the hit in pinpoint mode is a false positive so I filled the hole in. Hopefully the HF pinpointer will keep me from having this kind of problem in the future... at least until I can afford one of those Garrett pro pointers. What was weird was I checked the hole again before digging and the hit definitely appeared to be in the center of the hole still even though the staple ended up being in the side. I don't know if something about the shape of the staple was throwing it off or what (as the hole was almost 8 inches below where the staple was found so it shouldn't have been halo effect from rust in the dirt since the dirt wasn't in the hole at the time).
I would like to thank everyone for their advise in this thread. Being as I am new to the hobby I would expect to see more questions from me later.