So you're not actually measuring resting heart rate, just average non-active heartrate. Those sounds like two different things.
My FitBit HR (also using an optical sensor) says my resting HR has varied between about 52 and 59bpm over the past 5 weeks, which passes the sniff test. I tend to be in the high 70s/low 80s when standing and moving about, but when I sit down (to work or relax or whatever), it drops into the low 50s. One that really sticks in my mind was the day I did a free go karting session courtesy of blood donation. Wisely, they had us race first, then donate. I got out of the kart, walked to the waiting area, sat down, and 5 minutes later was called back and given a resting HR of 42.
My FitBit HR (also using an optical sensor) says my resting HR has varied between about 52 and 59bpm over the past 5 weeks, which passes the sniff test. I tend to be in the high 70s/low 80s when standing and moving about, but when I sit down (to work or relax or whatever), it drops into the low 50s. One that really sticks in my mind was the day I did a free go karting session courtesy of blood donation. Wisely, they had us race first, then donate. I got out of the kart, walked to the waiting area, sat down, and 5 minutes later was called back and given a resting HR of 42.