Thinking back to when my kids were infants, I wonder if dad wasn't in the shower.
Possible scenario: babies are napping. Mom goes to nap. It's summer, they went on an afternoon outing, and it's likely that Dad hadn't had a chance to shower that morning (I remember how hard it was to get a shower in those early weeks, and I only had one infant at a time to deal with). Dad goes to take a quick shower, one of the babies wakes and starts fussing, and NV volunteers (as worded in the reports) to change his diaper so Dad can hop in the shower. By the time the diaper is off, Dad is in the bathroom with the water running. NV isn't going to leave the diaper off until Dad is able to come look, so she takes a quick photo and sends it before cleaning the baby up with wipes and proceeding with the diaper change.