A child born abroad (out of wedlock) to a US citizen father is a US citizen, but there are a bunch of requirements to check off.
These jokers want the law for a child born to two married USC parents to apply.
The issue is not one of discrimination, the issue is that the law requires a biological relationship in this case, which only one of them has.
I think you missed the part that states that the biological father is not a citizen, just merely same-sex married to the naturalized US citizen. They appear to have deliberately used an innocent child to try to force a change to US law.