If someone offers to pay your medical bills after an accident, that act of kindness cannot be used against them in court to prove they were at fault. For example, if a driver hits you and offers to cover your hospital costs, a jury will never hear about that offer as proof the driver was responsible.
This rule exists so people feel free to help cover medical costs without worrying it will hurt them in a lawsuit. Without this protection, someone might refuse to help pay for medical care just because they fear it would be used as evidence against them.