Who really cares? A low resting HR can be due to fitness, sick sinus syndrome or a combination of both. In my case, at age 78, my resting HR was at 34, but an inserted monitor in my chest indicated pauses of up to 10 seconds, so I now have a pacemaker to maintain the resting HR at 60 and my biking performance is unaffected. So, if you are getting on in years, don’t be complacent about a low resting HR.
As someone wrote earlier, an indication of a healthy heart is how quickly it returns to a normal level. A guide is two minutes.