J.S.
I think maybe it just hit him how very much he loves that baby, and how important her needs are to him. It's very overwhelming when that realization hits. Let him feel it... because he clearly needed to feel it. It means he's bonding really well with her and it's a very good sign he feels that way.
Something else, though. It sounds to me as though the baby got extremely overwhelmed and overstimulated herself. She was probably showing early signs of being overstimulated, and it was great that you took her into a dark, quiet room, but I probably would have left with her sooner when she started showing signs sooner. Maybe time the visits for how long you know she can handle them and leave before you suspect a meltdown. Just a suggestion, not a criticism.