Indeed. There actually is a context. This is not about bringing up religion is some random unconnected thread. And the other moderated matter was another poster bringing up the atrocities and other problematic content in the source material. This is the sort of thing we talk here about a lot: how to deal with potentially problematic content. It is rather bizarre that the subject matter being connected to a religion would somehow make such an examination inappropriate.
I think the honest answer is ... it's difficult. There is a very good reason that this board has a no religion rule- from the T&C:
And in this category I should mention the "no religion, no politics" rule -- please refrain from discussion of a religious or political nature. This last may seem a rather draconic rule, but it has helped keep the peace around here for a long time. There are plenty of places on the internet where one could have those sorts of discussion.
Which is a great thing! Because ... yeah those don't tend to go well.
But then we get into issues when we do have the intersection of valid forum topics (in this case, a 5e setting based on Biblical themes) with a desire to not have the thread go off course. I don't think that there's an easy answer.
I would agree that it's further complicated because, in this case, people are more familiar with this specific issue. In the past, we've had a specific poster who adheres to less mainstream beliefs (Neo-Norse? I'm not sure how s/he prefers to describe it) that felt marginalized in conversations.
I don't think there is a single correct answer to this. In the end, the unsatisfying, but correct, answer is that this is similar to a dinner party at someone else's house, and in the end you have to pay attention to rules of the host of the party.