The plan with the highest premiums still has a deductible in the many thousands of dollars - far exceeding the $500 charge in question.
In Covered CA the x-ray is not subject to the deductible but has a $65.00 co-pay but the E-R visit is subject to the deductible with a $250 co-pay after the deductible. The $500 was probably ER and x-ray.