From the nature article, it seems this was the first video of natural bidirectional lightning, not triggered by rockets or aircraft: "In contrast to studies of rocket-triggered lightning and lightning initiated by aircraft, which found delays of 3–6 ms between the onset of negative and positive leader branches, this natural event exhibited a delay of less than 90 μs (i.e. one video image)."
This was a negative polarity lightning strike. the most common type. Less than 5% of lightning is positive polarity but they can carry ten times the charge and exceed a billion volts of potential.
When you read about people surviving lightning strikes it's almost certainly a negative polarity strike. https://en.wikipedia.org/wiki/Lightning#Positive_and_negativ...