Great question; the short answer is you can ignore the email from Training Peaks. Training Peaks uses pace and HR to determine your “New Threshold Heart Rate,” It has nothing to do with your Aerobic Threshold test. I frequently would get these notifications when I would forget to turn my watch off and jump in my car, for example.
As for your HR zones, Carolyn and I did a zoom on as our second zoom where we go over what Default Threshold means. Pretty much that is your Anaerobic Threshold (AnT), also known as the top end of Zone 3. If you were with us during that zoom, you might have filled in that number based on our recommendations. Training Peaks is a wonderful tool, but it doesn’t know its athletes aerobically very well at all.
I hope that helps!