It's this sort of attitude that makes people reluctant to help anyone else. Why bother, when - whatever you do - it's going to be dissected and bitched about by judgmental twats online?
Mumsnet is full of people who go into hysterics if someone smiles at their toddler or rings their doorbell. MNetters want a world where no one interacts with anyone else without prior permission yet, at the same time, a relative stranger is supposed magically to know when one of their neighbours is in trouble and intervene immediately.
It's easy to be wise in retrospect. You have no idea what you would have done, if confronted with the same situation in real time. I doubt many people would have leapt to the conclusion that Nicola had gone missing, when her phone and dog were right there.
The poor woman who found the phone must feel bad enough, without millions of twunts slagging her off. Stop it - you're just showing up your own inadequacies, lack of imagination, and general twatishness.