The correct stat is "50% of all bankruptcies include medical debt". That doesn't mean the medical debt caused the bankruptcy. It could be a $10 co-pay they didn't pay, but the $50,000 in credit card debt that sank them.

Keep in mind, health problems are actually a major cause of bankruptcy in countries with universal coverage like Canada as well. It's nice when your healthcare is paid for, but if you can't work, bankruptcy is a major problem as well.