Washington Medicaid. Hospital bill for labor + delivery? Illegal?

Hello just a question. My partner recently gave birth to a baby at a Medical Hospital in WA. We were transfered from a Birth Center due to being >36 hours since her water broke without signs of labor and thus requiring medical induction. Our midwife called to the Charge Nurse and CNM at the hospital and they accepted transfer of car so we were sent to the hospital. We went into the hospital through the ER and were picked up by labor and delivery. Now about a week later there’s a medical bill balance of $1800 in her Mychart as well as ~$6K pending if insurance doesn’t accept the pending claim for the difference. She signed documents as shown. But we are very confused because she has Washington Medicaid (Free medicaid with no copays etc). We thought according to WAC 182-502-0160 it was illegal to bill Medicaid customers for difference between insurance amount and what hospital deems it should charge. Is this not true?? They didn’t inform us about not accepting medicaid or anything and they’re an emergency department, etc. Also it says that the provider is responsible for knowing the limitations of the services and informing the client. Does something she signed magically erase this even though she had to sign these papers?

(https://apps.leg.wa.gov/wac/default.aspx?cite=182-502-0160)