Apple watch heart rate monitor

I was getting a physical the other day and was in doctors office. I told him that my resting heart rate was typically below 35 (as measured by Cardio App) each morning when woke up, and was still in bed. I said the apple watch at the same time typically read about twice that amount. I asked if he knew why. He had me on his monitor, and it at the time read about 40. (I had ridden my bike to his office.). He manually measured my pulse and confirmed about 40. However, my apple watch read about 75. He said: “you need to tell this to Apple. They need to know that their watch is not correctly reading pulse rate. Perhaps it is because your heart rate is extremely low, and it is not set up to read such out of norm rates. You have a low heart rate because you are so physically active, but the apple watch should still provide a closer match.” Thouhts?