I don't see them discussing the definition of "resting metabolic rate" in this paper. I don't know how long it takes the body to reach the "resting metabolic rate" though I imagine it varies depending on quantity and intensity of physical activity.

What I'm getting at is that people are more likely to drive to the doctor than they were in the past, which means they actually were likely at a truly resting metabolic rate when arriving at the doctor's office. While in the past, it's more likely people might have walked (or ridden a horse) a mile or more to the office, which I imagine would result in the "resting rate" to often not actually be a resting rate but be somewhat elevated.