Not true at all. Lightning strikes often leave very little evidence. In particular, if the ground was wet and rocky, a strike some distance away could easily have electrocuted the family with no or minimal burning, and the actual strike location could be nearly impossible to find.
I've seen this with my own eyes. A couple of years ago I watched lightning strike a tree in the park across the street during a rain storm. Afterward the tree showed no evidence of the strike except for some bark blown off. There was no visible burning on the tree or the surrounding ground, but I guarantee that anyone standing near that tree would have gotten zapped.
Was talking to a vet, they claimed that most cases of herd's dying "from lightning" were botulism related or other poisonings. The herds graze together, and can die together.
But this is an extreme symptom of a direct or nearly direct hit. Many lightning victims have no visible injury.
Lightning isn't very good at killing people, but it's capable of hurting you from a great distance, because it takes so little current across your heart to cause problems. There is evidence that as little as 5 mA can cause cardiac arrest, and this is the rationale for GFCI protected outlets in homes:
Not always. We lost two horses to a lightning strike and if not for us being there at the time, we'd have had no idea why they died. They were both lying dead on the ground with a mouthful of grass and no signs of injury.
