The Fairfax County police helicopter is also a medical transport. They fly with a pilot and a flight officer who is also a certified paramedic. You can read more about "Fairfax 1" here:
http://www.fairfaxcounty.gov/police/helicopter/
Helicopter transports often take place at schools because there is enough room to safely land a helicopter. The firefighters are responsible for setting up the landing zone. Most likely the patient came from some place other than that school.