It is exactly that dialogue, where they are talking about this impossible situation.

Also even if the servants cry Lostbelt, Moriarty explicitly talks about Romanis true identity being hidden. So even if that event did indeed happen, it needed to be prior to Solomon (well, that's a given, since Romani is alive, but you know what I mean).

I have two theories regarding that last dialogue.

The first is that the singularity is happening in the present and the singularity itself is allowing us to see Dr. Roman.

And the second is the other way around, it is happening in the past (before Solomon) and it's showing us future Servants.

In both cases we are oblivious to the small errors just like we don't notice the minor plot holes the movie we are filming has.