When you say medical flight, could it have been a 'Helimed' callsign?
I don't know if it's standard, but the Air Ambulance around my home area uses a callsign suffix to denote their mode of ops. 'Helimed 99 Echo' is used on an emergency, 'Helimed 99 Alpha' is for positioning afterwards... might it have been that, i.e. ATC querying the suffix?
Just a theory and it may/may not be the right answer in this instance.