I don't think you can know without a constant monitoring of system. I suspect because of the frigid temps, this was your auxiliary kicking in rather than defrost calls. A light indicator is usually on good heat pump thermostats that will display for both emergency and auxiliary heat. Of course the emergency heat will also activate on defrost calls to temper the incoming AC air.

IMO

He is right. You may not know that unless you monitor your system constantly. As for the heating measures, I don't think there is some problem with the system. The auxiliary must surely be kicking in from to time.