Like I said in my post, I was an electricians apprentice years ago, and I gladly took a step back and called a licensed professional when I ran into something I’d not seen. I used to do commercial new construction and worked with large generators, transfer switches, and general wiring, so this stuff isn’t new to me, but my house is new to me.
The end result here is that everything is put back the way it is with the notable exception of a Romex run that’s no longer end-to-end but spliced. I’m just questioning the little amount of voltage on a ground, which isn’t normal in a properly wired home.
Is your an older house? Sometimes in older houses they would wire all the light to a common ground and then a single hot wire to the switch. So, even though the breaker is ff to the switch you are working on, the ground could be being back fed from another fixture that would still be hot.
Is it voltage on a ground wire - green or bare copper - or on the white “neutral” wire. Voltage on a ground wire is asking for a lot of trouble and it’s amazing anything actually works. The white wire is “ok” except that it is backwards and therefore unsafe. It should be the black wire that is HV and the white wire should be grounded, though it is not a ground wire.
Also, get one of those little voltage detecting “pens” that beep and lights up when you touch it to a HV wire. First make sure it works by touching it to a live wire and then check everything around the circuit, outlet box etc. that is supposed to be “dead” to make sure it is really dead. And then check it again to make sure it is working. And check with a voltmeter as well. The advantage of the pens is that they will go off even when you cannot reach all the wire nuts or when you think everything is dead, but it turns out that there is another circuit coming into a box (multi-floor light switches in staircases are a huge problem this way)
Smart man; you know enough to know when you don’t know enough, AND you fully appreciate the cost of getting it wrong. I never feel bad about being too careful with electricity.