Med C is the 800mhz trunked talkgroup for Dorchester County units on the med radio. Look in Dorchester County's database and it will be listed along with Medcall and Med D for Dorchester units. Any further questions PM me and I will try to help you figure it out.
Talbot Center dispatchers will assign MED-C or MED-D when talking to Dorchester Co paramedic units requesting a patch to "1000" (Easton Memorial) or "DGH" (Dorchester General). I believe the reason you can hear this is because MED-CALL gets simulcasted on both Eastern Shore Consortinum TRS and Dorchester TRS.
Working channels MED-A/MED-B exist only on the Eastern Shore Consortium TRS, while MED-C/MED-D exist only on Dorchester TRS.