, you're right. I was theorizing. The title strongly suggests that it is better
than walking, say, in the mall or through your neighborhood. Yes, the terrain could make a difference. If we assume that both routes are equally level/flat and equally solid, I doubt there would be any difference.
The additional statement, "_Scientists have advanced a wide range of theories about the specific physical and mental benefits nature can provide,..._" uses the word "can", indicating that they have nothing to back up the suggestion they want you to believe. They seem to be throwing bait out for people to bite it at face value.
My thoughts? One should walk wherever they want and not let studies and reports like this deter them their neighborhood treks in favor of a wilderness stroll. No need burning gas getting to a forested area.
As for the study, if it's on one's own dime it would be interesting. If the government would fund it, nope.