You can be homophobic without opposing gay marriage (regardless of if you use "marriage" as the word), just like you can be racist without thinking black people shouldn't be allowed to get married. It's about attitude, not actions - the fact that he isn't trying to force his homophobia on others is what makes him the better kind of homophobe.
Well, perhaps the word doesn't carry the same negative weight that it does in portuguese. Here if you tell me someone is an homophobe, I imagine people that want to beat all homossexuals passing in the streets.