The resident is working under the teaching physician, so their charges would be one charge and not listed separately. Remember when they are billing with Modifier GC the resident is stating that the services were performed by a resident under the direction of the teaching physician. The claim would be billed with the resident as the performing, with the teaching physician as the supervising with GC modifier on whichever code is appropriate based on the services rendered.
The only other thing I can guess based on the information provided is that the teaching physician was working in the ER and saw the patient at the time that they presented under the 99284. Then a determination was made to admit the patient under observation (99218) where the services of the resident came into play. However the same provider should not be billing a 99284 and a 99218 for the same date of service for the patient.