Y'all have to remember posters here have limited knowledge....just like we do because we are not there....on problems posted.

If the thermostat was set to gas.....then the thermostat allows the furnace to control the blower which is a NO-NO with a heatpump. However, electric resistance does control the blower. maybe the blower comes on when the electric heat cycles...electric heat turns blower on....heatpump continues to run....electric heat satisfies turns off blower...heatpump continues to run....

usually heatpump squeals like a pig when this happens....but since I am not there to see what is actually happening.....