When you inadvertently spawn 537 children, odds are there are going to be quite a diverse group of children being produced (and at least one or more mixed race and/or homosexuals).
I mean, he was surprised to see the picture of the black girl in the stack and seemed quite shocked to see one of his sons kiss men!
ALL dads are surprised to find out that one of their sons likes other guys to no matter what degree. Plus, it would be a shock to find out that one is black because that isn't the first thing that comes to one's mind no matter the probabilities in said scenario.
It might depend on whether or not he'd ever dated inter-racially. I've known people who tend to date primarily people of a (different) specific race. I suppose when they think of children in their future they imagine mixed race children.
Also, skin colour is a tricky trait. I have a friend of colour that has four siblings, all with the same biological parents. They range from very pale, paler than many whites to very dark, almost black rather than brown. The birthmother could have been very light skinned of mixed race and might have been quite surprised at the skin tone of her daughter... or the clinic may have messed up and used the wrong specimen.
As to the gay aspect... it's possible that he's always been a bit girl-crazy and just never considered it.
I don't think he was shocked that the son was gay, but that he was a player. At that point he was following around trying to help each kid in a small way.