Clotting, and most likely myocarditis, are caused by bad antibodies. Infection causes antibodies too. There is most likely a much better quality control of antibodies if a real infection is going on, but we don't know the mechanisms yet. C19 is a cardiovascular decease. But if it was so bad that it damaged your heart, you know that and you'll be careful. When vaccines induce myocarditis, most people don't feel it, the heart attack comes as a surprize later.