And now it really gets his goat.
BTW, I don’t see anyone saying that Opal was wrong to begin with.
At any rate, I can’t find any justification for saying that numbered lists must have at least three items in my Chicago Manual of Style. Why would anyone make this claim? It seems like a silly affectation to me.
It’s now in the Chicago Reader Manual of Style. 
My WAG is that if you do not have 3 items to list, then a simple “A & B” in a sentence or two suffices. Using a list of bullets or numbered points when an either/or works is a bit silly.
"The differences outlined in the discussion basically came down to using two or three items in a list.
-vs-
The differences outlined in the discussion of how many items should be in a list basically were:
- Two
- Three
- Hi Opal!"
-Tcat
Asked and answered.
TubaDiva