I'm guessing that in those days people spent a large amount of time walking (not car based living), work had a lot less sitting down and there was more manual labour (including simple things like cleaning without machines). For a fully active life like that 3.5K is I guess about right for an adult male? Perhaps ... it sounds like a high estimate to me.
Discussion
Yeah I'm 100% sure you are right about that but also I believe it's the quality of the food people ate then versus now. I think the processed food and probably the seed oils we eat now is causing a lot of our health and weight issues. I think single ingredient foods are the key to changing that.