That's what I said. "Not that it matters". They are married depending on who you mean by "they".
"And yes, it does matter because only certain groups automatically pass citizenship on to their kids..."
It matters who the legal parents are. It doesn't matter who is married.
"Again, look at woodpusher's post. If one parent is an alien, the other has to be a citizen, and have been physically present in these US for a minimum five years..."
Yes, that's true. When I looked it up the first time I actually found a page showing US Code that said something different. But I acknowledge this version is the correct one.
So the one biological parent is a citizen, and can pass that citizenship on as long as they meet the residency requirement. The State Dept is saying they don't. But there's nothing in the code about "wedlock", so I don't know where they get that bit.
Clearly this case is about whether the second parent is the biological mother or the partner of the biological father. Who the law sees as a parent is often not a biological question though, and adoptive parents are legal parents. I don't see this case as very remarkable.