The "wild environments" offer concrete examples of the benefits of solitude. They're reduced anxiety, not being on pills, boosts to your the immune system, etc. Solitude generally accompanies the wilderness, and wilderness is the tangible gateway to the insight and humility you might gain from solitude.
But of course the wilderness doesn't strictly mean not socializing. Talk to anyone who's thru-hiked the Appalachian Trail or similar and you'll hear about how social of an experience it was, between the times of solitude. The thing is that there is no solitude in heavily populated environments, where things like work are what you're supposed to do. This is the point of the article: in cities, in society, you're not able to focus on the simple joy of your existence, as Byrd was. In solitude you're free from the urban burdens and obligations that stress us, despite how well we've adapted to them.
The Appalachian Trail isn't wilderness. I recall reading somewhere that by some definition related to road building (if memory serves) there is no true wilderness in the lower 48. Alaska is it for the US, at least by that particular definition. Sorry, no citation.
You have to go into some parts of the Rockies for what wilderness remains in the lower 48. I've fished some alpine lakes that likely hadn't seen any human in a year, if even.
The road rule is actually part of why certain groups push to build roads on public lands, because it reduces the land's environmental status and access to protections from exploitation.
When I lived in Montana, I would regularly hike trails that clearly hadn't seen someone in at least a year, sometimes several, and this was only a little ways outside of Bozeman. I am unfamiliar with the road-building/true wilderness definition, but I can confidently say that there is plenty of wild to be found in the lower 48, by any reasonable assessment.
But of course the wilderness doesn't strictly mean not socializing. Talk to anyone who's thru-hiked the Appalachian Trail or similar and you'll hear about how social of an experience it was, between the times of solitude. The thing is that there is no solitude in heavily populated environments, where things like work are what you're supposed to do. This is the point of the article: in cities, in society, you're not able to focus on the simple joy of your existence, as Byrd was. In solitude you're free from the urban burdens and obligations that stress us, despite how well we've adapted to them.