If I knew that my family member had been self-isolating except for a routine bike ride, and they had not come back by their usual time - yes, I would call 911.
Further, having lived in some isolated places and still keeping track of crime in the place I used to live, I'd be even more likely to do so. However, the Morphews hadn't been there that long (according to BLM's MSM information he became a volunteer fireman in August 2018, but they didn't buy the house until December - so presumably, they had only had about 17 months of local residency).
There were virtually no other humans living near their house, IMO. There's no place to "just stop by," IMO, except the neighbor whose house was called. However, it would be strange indeed for a woman who had been battling cancer and is probably still on some medication to risk breaking quarantine.
Ending up having dinner? During self-isolation? In that case, Suzanne would indeed be an extreme risk taker and if I were her spouse, I'd want to know what she was up to, that she'd risk her incredible health progress for dinner. Anyway, if we're just going to use our own notions about common sense, I'd say that yes, a spouse should be concerned if their spouse is out and about, in an unexpected manner, during CoVid self-isolation.
You can look up the residency situation of the other buildings in that little area where she biked. If she had completed her ride, it's my opinion that she would have encountered no more houses - only campsites.
I'll add one more risk factor, just in case other people don't worry about such things. Being one of the richest people in an area (as judged by locals eyeing your digs) is not the safest position on the social pyramid.
Keep in mind that it was the daughters who called the neighbor. Clearly, they expected to talk to their mother on Mother's Day (IMO). Then the neighbor for whatever reason (missing bike? finding the bike?) calls 911. The neighbor knows way more about the situation than we do.
