Sudden death due to cardiac events in young, otherwise healthy people, is not a new phenomenon. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4969030/

Anecdata time: the nurse at the school I attended in the 90's had a son who was a marathon runner, keel over and die on a light training run from a undiagnosed heart defect 30 years ago.

If you're referring to Damar Hamlin, if you look at the event he took a super hard blow to his chest prior to collapsing, something which can cause a cardiac arrest.