That's because he generally applied, but refused to accept, the legal definition of the un-modified statutory term "marriage" in the course of his business. According to corporate statutory law, the word "marriage" - when used in the general sense for corporate purposes - includes homosexual marriage. So to exclude homosexual marriages from the use of the unmodified word "marriage" in the course of business is illegal.
Under the current law, it's exactly the same issue as saying that you will serve the general public, but then exclude particular people because of age, race, sex or religion. You simply can't do that - "general public" includes all of those people by law, and likewise (these days) "marriage" includes homosexual marriage.
So that's why, if he wanted to restrict his application of his work for the purposes of the TYPES of marriages that HE wanted to bake cakes for, then he needed to SPECIFY that he would only do SPECIAL WEDDING CAKE ORDERS for marriages that were being done under certain religious traditions or churches that HE wanted to do them for - and no others.
And in addition, he would have to not, within the course of his business, say anything that would express rejection of homosexuality as a condition under which he was willing to do general business.
This kind of language counts. It's the way the world currently works. I'm not praising it, I'm just pointing out the fact of it. And I'm also pointing out that there is a way that Christians can not bake cakes for homosexual marriages that the law will accept. That's all.
I’ve read a lot of court rulings. Some judges follow the law. A great many simply “feel”, and rule based on their feelings. Words are just what they twist to justify ruling on their feelings.