Hitch a Ride

Within the last few months, I have had numerous walkers stop me on my jog asking if these two are twins. Also in the grocery store.
How did they come to this conclusion?
Different skin color
Different eye color
Different hair color
Different size
(may be the same in width to the questioning parties' defense)
On the other hand, when I look at a picture like this, I am taken back at how much they do, in fact, look a like.
I also experience a little heart flutter when something as simple as Kid's hand covering Baby's takes place. To watch these two as siblings become little buddies is such a gift.