Visual
Your comment appears correct regarding minimums when on a visual approach.
But, were they visually proceeding at the point of the runway in sight call?
At this time, there does not appear to be a confirmation by the PF that the runway was in sight, or that he was going to continue "on the gauges".
I'll have to re-read the time line about the call out and when things started turning bad.
However, there have been times when I have received a runway in sight call and my response was, "continuing on the approach", as I new that visual cues for that approach could be misleading. The approach to the west at San Diego comes to mind.
Just my opinion, but I don't think they slipped 200+ feet low because of that call out, or being on a visual approach at that moment.
Regards.