The state has a compelling interest to protect a consumers right to "reasonable expectations of service". It's a concept that undergirds much of contract and property law. A person has a right to the free exercise of their religion. The question is which wins in which situation.
Obviously the right to free exercise of religion is limited. As an extreme example, you cannot kidnap and murder someone because you're a practising Canaanite.
So which wins here? Lets find similar situations. If you are a baker then you are making a product used in an event. This is no different than manufacturing a sign, printing documents, making clothing, building furniture, etc.... And as you rightly point out, the question is not who buys these products, but how are they used. An easy way to see this is to ask yourself how the argument would change if a baker was asked to make a wedding cake by a straight couple, who then gave the wedding cake to a gay couple for a gay wedding. Would not any objection to providing a wedding cake to a gay couple not also hold if there was a middle broker? The baker can't then be objecting to selling a wedding cake to a gay couple, instead the baker must be objecting to a cake that they made being used at a gay wedding.
That means that the general form of the religious freedom in question here is the right for a manufacturer to restrict the uses of their products according to privately held beliefs. Can a Christian table cloth manufacturer ban the use of their tablecloths at a gay wedding? Clearly not. Not only does the states interest outweigh whatever supposed religious freedom this company has, but examine the path of any enforcement. The manufacturer would have to bring suit against the gay wedding on the grounds that the use of their tablecloths was a violation of their religious freedoms which resulted in monetary harm.
I doubt any court would find this compelling.