So in the conspiracy theory version of reality you are touting, how would the customer know ahead of time that the baker was anti-trans enough to not want to make the cake?
You said you didn't read the thread... so clearly there's a lot you are missing. That's fine. But don't go inventing things and speculating like this when actual information exists.
The lawyer contacted this baker specifically because this baker specifically had previously won a suit regarding a same-sex marriage cake. The lawyer has been after this specific baker for a while. The lawyer specifically told this specific baker that the colors of the cake symbolized the lawyer's gender transition. The baker has ideological or religious objections to gender transition, and refused to bake the cake. According to the baker, he would not bake any cake for a gender transition celebration, if he knew that was the purpose to which his creation was being put.
While it is certainly reasonable to be skeptical of what the baker would do in other circumstances, there is currently no evidence to suggest that the baker would not sell a cake for a different purpose to a person who is transgender. Thus, the baker argues that he is not discriminating against the person or their identity, he is refusing to engage in compelled expressions of support for something he does not, in actuality, support.