I got the below explanation from DC Rainmaker. I think it might clear this up...
The lowest HR of your day is commonly referred to as your resting heart rate (RHR). Now technically speaking, per most…
I am 45 and in decent shape and I rarely get below 52 on my resting heart rate. Maybe you have better genetics? I've always heard that a lower resting heart rate was a sign of good fitness but I'm definitely not an expert. I also don't fully trust wrist based heart rate monitoring. I find at least for exercising that the chest strap is significantly more accurate. It's not even close.