You may already have seen this if you looked down the hole at any point, but to add to the mystery, your terminology of it being "keyed" is not far off.
The 180 degree one way or the other thoughts are likely from GM products (if you've ever worked on or read about those) that simply use a "blade" like a screwdriver on the end of the shaft that slips into a matching slot in the oil pump shaft.
Ford uses a hex-shaped shaft, instead of a slot, so you can get it one tooth off on the gear and not quite be able to seat the female distributor shaft in the male pump shaft.
To make it work for you then, you can either stick a tool down the hole to spin the pump shaft slightly, or rotate the engine slightly until they line up, then backtrack to the marks. Whichever way works to get you lined up and working is fine.
Obviously, you got that figured out and it's in and running. I just wanted to mention that in case you had not had a chance to look down the hole and see what was going on. Or needed to do it again to get a better distributor body/cap alignment for your particular setup.
And like was said, in a 4-stroke/cycle engine, the cam, and therefore the distributor, rotates at half the speed of the crank. So your TDC marks come up twice for every one rotation of the distributor.
That's what is meant by getting the distributor 180 out, or off.
But if your timing light shows your marks lining up and you're running, you're at least in the ballpark and not 180 off.
Paul