Lightning can strike well ahead of, or behind, a storm system. 5 kms is really not enough to ensure safety. See this article -
Lightning Detectors Provide Early Thunderstorm Warning and Save Lives
Lightning is also unpredictable - even sneaky. While most strikes occur close to the rain, hail and winds of a thunderstorm, a significant proportion occur well before or after the main part of the storm has passed. For more information visit the
Lightning page.
Strikes 10 miles (16km) or more ahead of the storm are not uncommon, and while the storm may be visible in open country, at this distance thunder may not be heard. These sorts of strikes are often referred to as "bolts from the blue"
(my emphasis)
I have observed a lightning strike just over my back fence when the associated storm was about 10 miles away. It was a very small bolt, but probably could have killed. There was no associated thunder. I was mowing the lawn at the time, rushing to finish before the rain. Needless to say, I packed up immediately & hightailed it into the house!
I think this could be an explaination as to why people get struck on golf courses, on the beach, in the park, etc. They think that because the storm is in the distance they are safe. It would also explain why a number of these victims survive, with the lightning bolt being very small.