Just my opinion:
Standing is more stressful than walking. Walking keeps the circulation moving. Concrete is indeed worse than dirt. Also, being out in nature is more nourishing to the mind. Fresh air vs. indoor air might be an issue as well.
One summer I was having issues with my hip. Standing on the deck at the hiking lodge while waiting for the guide to be ready made the hip hurt. (The guides had chores to do after breakfast, so were never ready before us, and often the benches would be wet from dew or rain overnight, so I could not sit down.) Once we got out on the trail the hip pain cleared up and mostly was okay during the hiking. So I think that standing is more stressful than walking, even though walking is more work.