It says "a leading cause", not "the leading cause". Depending on how long your list of leading causes is, anything could qualify.
I skimmed the source they linked, and it lists guns as the leading cause of death for ages 1-19. I did not see an overall list.
I would agree that a more carefully phrased sentence would have been better and less misleading.
Link to source: https://publichealth.jhu.edu/sites/default/files/2022-05/2020-gun-deaths-in-the-us-4-28-2022-b.pdf
Many people who are born go on to have children of their own. So a single pregnancy can lead to generations and generations of deaths!