After two years of zombie killing, it's become so common place that just saying " I killed them" is sufficient without any further explanation.............
Here's an example: I destroyed a nest of wasps yesterday.........Do I need to go into detail as to why I destroyed it?
Well, killing people is still different from killing Walkers. And it seemed pretty clear that Carol and Rick were both talking about Karen and David — not Walker Karen and Walker David. If she had killed Walker Karen and Walker David then nobody would really care all that much.