well just like she said that they used to worship after all beside he already live that long while keeping the radical faction at bay so you can be sure he is strong that former demon king
It was hinted earlier on that Noir is probably an isekai character himself, not really a reason so much as maybe a hint at what Noir may do later in the story. From what I've seen throughout this story is that the author may be a bit lacking in the display of relationship advancement, but where he lacks there he makes up for in his mid-range foreshadowing. In this arc some super early foreshadowing was cashed in even.