There were three pictures in that post. The top one and the left side of the third one were claimed to be dated in approximately in the late 20s. It's hard for me to imagine which of the two from that late 20s era could have been taken in the 70s! Could you help me better understand what you mean? Is there a typo somewhere?
In the bottom picture, GHS, Jr. (at left) was in his teens, as was the picture of his grandson (on the right). Wikipedia notes that the larger family picture from which that grandson's image came was taken in 2005.
Color pictures until the 70’s were the work of professionals. This photo has the feel of a 70’s era Kodak. I think it’s a typo in the caption.