Why do men get a "woody" when they kiss(make out) with some girls but don't get when they kiss others?

I have this friend (a guy) and we have been friends ever since we were kids, so are very open to one another.

The other day he told me something that got me intrigued. He did this play in his college theater and kissed (made out, without using tongue) with a rather pretty girl.

Yet when I asked him how it was he said it was sort of bland, and that he did not get an erection the way he does he kisses his girlfriend.

I thought ALL men got aroused when they kissed ANY girl they found pretty. He explain to me that it does not work like that (not for every men at least).

He said that in his case, already having a gf he is really into made the experience a lot less exciting that it could have been. He said some guys need more than just looks from a girl, and that some guys need to feel a connection with the girl.

I am confused because that's not what women learn about men. We learn men are visual and that the mere sight of a woman may arouse them. We never hear anyone say some men need to actually like the girl for it to happen.

Can anyone clarify this a bit more for me please. I appreciate serious answers.

PS.: If it matter, he is 34 yrs.