Announcement: I hold, at the very least, that the trinity is Avodah Zarah Mamash and that the word should be Assur to say in the referring to Christianity, for whatever that’s worth.
And just a question on this whole Ma’aseh. If you had picked it up, you wouldn’t have done anything wrong (unless you knew of this key thing beforehand). Why does it matter whatever Shtus this person had in mind?